Encoder, decoder, encoding method, and decoding method

ABSTRACT

Provided is an encoder which includes circuitry and memory. Using the memory, the circuitry splits an image block into a plurality of partitions, obtains a prediction image for a partition, and encodes the image block using the prediction image. When the partition is not a non-rectangular partition, the circuitry obtains (i) a first prediction image for the partition, (ii) a gradient image for the first prediction image, and (iii) a second prediction image as the prediction image using the first prediction image and the gradient image. When the partition is a non-rectangular partition, the circuitry obtains the first prediction image as the prediction image without using the gradient image.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of U.S. applicationSer. No. 17/725,106, filed Apr. 20, 2022, which is a U.S. continuationapplication of U.S. application Ser. No. 17/724,178, filed Apr. 19,2022, which is a U.S. continuation application of U.S. application Ser.No. 16/942,630, filed Jul. 29, 2022, which is a U.S. continuationapplication of PCT International Patent Application NumberPCT/JP2019/003065 filed on Jan. 30, 2019, claiming the benefit ofpriority of U.S. Provisional Patent Application No. 62/623,834 filed onJan. 30, 2018, the entire contents of which are hereby incorporated byreference.

BACKGROUND 1. Technical Field

The present disclosure relates to an encoder and related technologiesfor encoding an image block.

2. Description of the Related Art

Conventionally, H.265, which is also referred to as high efficiencyvideo coding (HEVC), has been known as a standard for encoding videos(Non-Patent Literature 1: H.265 (ISO/IEC 23008-2 HEVC)/HEVC (highefficiency video coding)).

SUMMARY

An encoder according to an aspect of the present disclosure is anencoder which includes circuitry and memory. Using the memory, thecircuitry: splits an image block into a plurality of partitions; obtainsa prediction image for a partition included in the plurality ofpartitions; and encodes the image block using the prediction image. Inobtaining the prediction image, the circuitry: determines whether thepartition is a non-rectangular partition; when the partition isdetermined not to be a non-rectangular partition, obtains (i) a firstprediction image for the partition, (ii) a gradient image for the firstprediction image, and (iii) a second prediction image as the predictionimage using the first prediction image and the gradient image; and whenthe partition is determined to be a non-rectangular partition, obtainsthe first prediction image as the prediction image without using thegradient image.

Note that these general or specific aspects may be implemented by asystem, a device, a method, an integrated circuit, a computer program,or a non-transitory computer-readable recording medium such as a compactdisc read only memory (CD-ROM), or by any combination of systems,devices, methods, integrated circuits, computer programs, or recordingmedia.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a functional configuration of anencoder according to Embodiment 1;

FIG. 2 illustrates one example of block splitting according toEmbodiment 1;

FIG. 3 is a chart indicating transform basis functions for eachtransform type;

FIG. 4A illustrates one example of a filter shape used in ALF;

FIG. 4B illustrates another example of a filter shape used in ALF;

FIG. 4C illustrates another example of a filter shape used in ALF;

FIG. 5A illustrates 67 intra prediction modes used in intra prediction;

FIG. 5B is a flow chart for illustrating an outline of a predictionimage correction process performed via OBMC processing;

FIG. 5C is a conceptual diagram for illustrating an outline of aprediction image correction process performed via OBMC processing;

FIG. 5D illustrates one example of FRUC;

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory;

FIG. 7 is for illustrating pattern matching (template matching) betweena template in the current picture and a block in a reference picture;

FIG. 8 is for illustrating a model assuming uniform linear motion;

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks;

FIG. 9B is for illustrating an outline of a process for deriving amotion vector via merge mode;

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing;

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing;

FIG. 10 is a block diagram illustrating a functional configuration of adecoder according to Embodiment 1;

FIG. 11 is a flow chart illustrating encoding processing and decodingprocessing for an image block according to a first aspect of Embodiment1;

FIG. 12A is a schematic diagram illustrating splitting of the imageblock into four partitions according to Embodiment 1;

FIG. 12B is a schematic diagram illustrating a first example ofsplitting the image block into two partitions according to Embodiment 1;

FIG. 12C is a schematic diagram illustrating a second example ofsplitting the image block into two partitions according to Embodiment 1;

FIG. 12D is a schematic diagram illustrating a first example ofsplitting the image block into three partitions according to Embodiment1;

FIG. 12E is a schematic diagram illustrating a second example ofsplitting the image block into three partitions according to Embodiment1;

FIG. 12F is a schematic diagram illustrating a first example ofobliquely splitting the image block according to Embodiment 1;

FIG. 12G is a schematic diagram illustrating a second example ofobliquely splitting the image block according to Embodiment 1;

FIG. 12H is a schematic diagram illustrating a third example ofobliquely splitting the image block according to Embodiment 1;

FIG. 12I is a schematic diagram illustrating a first example of acombined way of splitting the image block according to Embodiment 1;

FIG. 12J is a schematic diagram illustrating a second example of acombined way of splitting the image block according to Embodiment 1;

FIG. 13A is a schematic diagram illustrating a triangular partitionaccording to Embodiment 1;

FIG. 13B is a schematic diagram illustrating an L-shape partitionaccording to Embodiment 1;

FIG. 13C is a schematic diagram illustrating a pentagonal partitionaccording to Embodiment 1;

FIG. 13D is a schematic diagram illustrating a hexagonal partitionaccording to Embodiment 1;

FIG. 13E is a schematic diagram illustrating a polygonal partitionaccording to Embodiment 1;

FIG. 14 is a flow chart illustrating ATMVP processing according toEmbodiment 1;

FIG. 15 is a conceptual diagram illustrating processing for determininga corresponding block in the ATMVP processing;

FIG. 16 is a conceptual diagram illustrating processing for deriving amotion vector for a sub-block in the ATMVP processing;

FIG. 17 is a flow chart illustrating STMVP processing according toEmbodiment 1;

FIG. 18 is a flow chart illustrating DMVR processing according toEmbodiment 1;

FIG. 19 is a flow chart illustrating a first example of encodingprocessing and decoding processing for a flag according to Embodiment 1;

FIG. 20 is a flow chart illustrating a second example of encodingprocessing and decoding processing for a flag according to Embodiment 1;

FIG. 21 is a flow chart illustrating encoding processing and decodingprocessing for an image block according to a second aspect of Embodiment1;

FIG. 22 is a flow chart illustrating encoding processing and decodingprocessing for an image block according to a third aspect of Embodiment1;

FIG. 23 is a flow chart illustrating encoding processing and decodingprocessing for an image block according to a fourth aspect of Embodiment1;

FIG. 24 is a block diagram illustrating an implementation example of theencoder according to Embodiment 1;

FIG. 25 is a flow chart illustrating a first operation example of theencoder according to Embodiment 1;

FIG. 26 is a flow chart illustrating a second operation example of theencoder according to Embodiment 1;

FIG. 27 is a flow chart illustrating a third operation example of theencoder according to Embodiment 1;

FIG. 28 is a block diagram illustrating an implementation example of thedecoder according to Embodiment 1;

FIG. 29 is a flow chart illustrating a first operation example of thedecoder according to Embodiment 1;

FIG. 30 is a flow chart illustrating a second operation example of thedecoder according to Embodiment 1;

FIG. 31 is a flow chart illustrating a third operation example of thedecoder according to Embodiment 1;

FIG. 32 illustrates an overall configuration of a content providingsystem for implementing a content distribution service;

FIG. 33 illustrates one example of an encoding structure in scalableencoding;

FIG. 34 illustrates one example of an encoding structure in scalableencoding;

FIG. 35 illustrates an example of a display screen of a web page;

FIG. 36 illustrates an example of a display screen of a web page;

FIG. 37 illustrates one example of a smartphone; and

FIG. 38 is a block diagram illustrating a configuration example of asmartphone.

DETAILED DESCRIPTION OF THE EMBODIMENTS

For example, when an encoder encodes an image block included in a video,the encoder splits the image block into a plurality of partitions, andperforms prediction processing on each partition. The encoder mayperform inter prediction on the partitions. The encoder then encodes theimage block using the result of the prediction processing. Specifically,the encoder encodes a difference obtained by taking away, from the imageblock, a prediction image obtained through prediction processing. Thisreduces the encoding amount.

When a decoder decodes an image block included in a video, the decoderalso splits the image block into a plurality of partitions, and performsprediction processing on each partition. The decoder may perform interprediction on the partitions. The decoder then decodes the image blockusing the result of the prediction processing. Specifically, the decoderreconstructs the image block by decoding the encoded difference andadding a prediction image obtained through prediction processing to theencoded difference. By doing so, the image block is decoded.

With regard to the splitting of the image block, splitting the imageblock into a plurality of partitions including a non-rectangularpartition is under consideration. However, when the image block is splitinto a plurality of partitions including a non-rectangular partition,the prediction processing becomes complicated, resulting in an increasein the processing amount.

In view of the above, an encoder according to an aspect of the presentdisclosure is an encoder which includes circuitry and memory. Thecircuitry encodes an image block using the memory. In encoding the imageblock, the circuitry: obtains one or more size parameters related to thesize of the image block; determines whether the one or more sizeparameters and one or more thresholds satisfy a determined relationship;encodes a split parameter when the one or more size parameters and theone or more thresholds are determined to satisfy the determinedrelationship, the split parameter indicating whether the image block isto be split into a plurality of partitions including a non-rectangularpartition; and encodes the image block after splitting the image blockinto the plurality of partitions when the split parameter indicates thatthe image block is to be split into the plurality of partitions. Thedetermined relationship may be predetermined.

With this, the encoder can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters related to the size ofthe image block and the one or more thresholds satisfy the determinedrelationship. Accordingly, the encoder can efficiently process the imageblock.

For example, the circuitry encodes the image block without encoding thesplit parameter when the one or more size parameters and the one or morethresholds are determined not to satisfy the determined relationship.

With this, the encoding amount can be reduced. Moreover, the encoder canreduce the processing amount for encoding the split parameter.

For example, the circuitry encodes the image block without splitting theimage block or encodes the image block after splitting the image blockinto a plurality of rectangular partitions, when the one or more sizeparameters and the one or more thresholds are determined not to satisfythe determined relationship.

With this, the encoder can reduce splitting of the image block into aplurality of partitions including a non-rectangular partition.

For example, the circuitry encodes the image block without splitting theimage block or encodes the image block after splitting the image blockinto a plurality of rectangular partitions, when the split parameterindicates that the image block is not to be split into the plurality ofpartitions.

With this, the encoder can reduce splitting of the image block into aplurality of partitions including a non-rectangular partition.

For example, the one or more thresholds comprise one threshold, and thedetermined relationship is that each of the one or more size parametersis greater than or equal to the one threshold, or that at least one ofthe one or more size parameters is greater than or equal to the onethreshold.

With this, the encoder can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters are greater than orequal to the one threshold.

For example, the one or more thresholds comprise a first threshold and asecond threshold, the first threshold is less than or equal to thesecond threshold, and the determined relationship is that each of theone or more size parameters is greater than or equal to the firstthreshold and less than or equal to the second threshold, or that atleast one of the one or more size parameters is greater than or equal tothe first threshold and less than or equal to the second threshold.

With this, the encoder can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters are greater than orequal to the first threshold and less than or equal to the secondthreshold.

For example, the non-rectangular partition is a triangular partition.

With this, the encoder can switch whether or not to split the imageblock into a plurality of partitions including a triangular partition,when the one or more size parameters related to the size of the imageblock and the one or more thresholds satisfy the determinedrelationship.

For example, the one or more size parameters include at least one of aratio of the width of the image block to the height of the image block,a ratio of the height of the image block to the width of the imageblock, the width of the image block, or the height of the image block.

With this, the encoder can use, as a size parameter, at least one of theratio of the width to the height of the image block, the ratio of theheight to the width of the image block, the width of the image block, orthe height of the image block.

For example, each of the one or more thresholds is greater than or equalto zero.

With this, the encoder can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters and the one or morethresholds, each of which is greater than or equal to zero, satisfy thedetermined relationship.

For example, the one or more thresholds indicate a restricted range of aratio of the width of the image block to the height of the image block.Here, the restricted range is a range for splitting the image block intothe plurality of partitions.

With this, the encoder can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters and the one or morethresholds, which indicate a restricted range of the ratio of the widthto the height, satisfy the determined relationship.

For example, a decoder according to an aspect of the present disclosureis a decoder which includes circuitry and memory. The circuitry decodesan image block using the memory. In decoding the image block, thecircuitry: obtains one or more size parameters related to the size ofthe image block; determines whether the one or more size parameters andone or more thresholds satisfy a determined relationship; decodes asplit parameter when the one or more size parameters and the one or morethresholds are determined to satisfy the determined relationship, thesplit parameter indicating whether the image block is to be split into aplurality of partitions including a non-rectangular partition; anddecodes the image block after splitting the image block into theplurality of partitions when the split parameter indicates that theimage block is to be split into the plurality of partitions. Thedetermined relationship may be predetermined.

With this, the decoder can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters related to the size ofthe image block and the one or more thresholds satisfy the determinedrelationship. Accordingly, the decoder can efficiently process the imageblock.

For example, the circuitry decodes the image block without decoding thesplit parameter when the one or more size parameters and the one or morethresholds are determined not to satisfy the determined relationship.

With this, the encoding amount can be reduced. Moreover, the decoder canreduce the amount of processing for decoding the split parameter.

For example, the circuitry decodes the image block without splitting theimage block or decodes the image block after splitting the image blockinto a plurality of rectangular partitions, when the one or more sizeparameters and the one or more thresholds are determined not to satisfythe determined relationship.

With this, the decoder can reduce splitting of the image block into aplurality of partitions including a non-rectangular partition.

For example, the circuitry decodes the image block without splitting theimage block or decodes the image block after splitting the image blockinto a plurality of rectangular partitions, when the split parameterindicates that the image block is not to be split into the plurality ofpartitions.

With this, the decoder can reduce splitting of the image block into aplurality of partitions including a non-rectangular partition.

For example, the one or more thresholds comprise one threshold, and thedetermined relationship is that each of the one or more size parametersis greater than or equal to the one threshold, or that at least one ofthe one or more size parameters is greater than or equal to the onethreshold.

With this, the decoder can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters are greater than orequal to the one threshold.

For example, the one or more thresholds comprise a first threshold and asecond threshold, the first threshold is less than or equal to thesecond threshold, and the determined relationship is that each of theone or more size parameters is greater than or equal to the firstthreshold and less than or equal to the second threshold, or that atleast one of the one or more size parameters is greater than or equal tothe first threshold and less than or equal to the second threshold.

With this, the decoder can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters are greater than orequal to the first threshold and less than or equal to the secondthreshold.

For example, the non-rectangular partition is a triangular partition.

With this, the decoder can switch whether or not to split the imageblock into a plurality of partitions including a triangular partition,when the one or more size parameters related to the size of the imageblock and the one or more thresholds satisfy the determinedrelationship.

For example, the one or more size parameters include at least one of aratio of the width of the image block to the height of the image block,a ratio of the height of the image block to the width of the imageblock, the width of the image block, or the height of the image block.

With this, the decoder can use, as a size parameter, at least one of theratio of the width to the height of the image block, the ratio of theheight to the width of the image block, the width of the image block, orthe height of the image block.

For example, each of the one or more thresholds is greater than or equalto zero.

With this, the decoder can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters and the one or morethresholds, each of which is greater than or equal to zero, satisfy thedetermined relationship.

For example, the one or more thresholds indicate a restricted range of aratio of the width of the image block to the height of the image block.Here, the restricted range is a range for splitting the image block intothe plurality of partitions.

With this, the decoder can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters and the one or morethresholds, which indicate a restricted range of the ratio of the widthto the height, satisfy the determined relationship.

For example, an encoding method according to an aspect of the presentdisclosure is an encoding method which includes encoding an image block.The encoding of the image block includes: obtaining one or more sizeparameters related to the size of the image block; determining whetherthe one or more size parameters and one or more thresholds satisfy adetermined relationship; encoding a split parameter when the one or moresize parameters and the one or more thresholds are determined to satisfythe determined relationship, the split parameter indicating whether theimage block is to be split into a plurality of partitions including anon-rectangular partition; and encoding the image block after splittingthe image block into the plurality of partitions when the splitparameter indicates that the image block is to be split into theplurality of partitions. The determined relationship may bepredetermined.

With this, it is possible to switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters related to the size ofthe image block and the one or more thresholds satisfy the determinedrelationship. Accordingly, the image block can be efficiently processed.

For example, a decoding method according to an aspect of the presentdisclosure is a decoding method which includes decoding an image block.The decoding of the image block includes: obtaining one or more sizeparameters related to the size of the image block; determining whetherthe one or more size parameters and one or more thresholds satisfy adetermined relationship; decoding a split parameter when the one or moresize parameters and the one or more thresholds are determined to satisfythe determined relationship, the split parameter indicating whether theimage block is to be split into a plurality of partitions including anon-rectangular partition; and decoding the image block after splittingthe image block into the plurality of partitions when the splitparameter indicates that the image block is to be split into theplurality of partitions. The determined relationship may bepredetermined.

With this, it is possible to switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters related to the size ofthe image block and the one or more thresholds satisfy the determinedrelationship. Accordingly, the image block can be efficiently processed.

For example, an encoder according to an aspect of the present disclosureis an encoder which includes circuitry and memory. Using the memory, thecircuitry splits an image block into a plurality of partitions, obtainsa prediction image for a partition included in the plurality ofpartitions, and encodes the image block using the prediction image. Inobtaining the prediction image, the circuitry: determines whether thepartition is a non-rectangular partition; when the partition isdetermined not to be a non-rectangular partition, obtains (i) a firstprediction image for the partition using a first motion vector for thepartition, (ii) a second motion vector for the partition using the firstprediction image, and (iii) a second prediction image for the partitionas the prediction image using the second motion vector; and when thepartition is determined to be a non-rectangular partition, obtains thefirst prediction image as the prediction image using the first motionvector, without using the second motion vector.

With this, the encoder can reduce the two-step operation fornon-rectangular partitions, and suppress an increase in the processingamount.

Accordingly, the encoder can efficiently process the image block.

For example, the circuitry determines that the partition is anon-rectangular partition when the partition is a triangular partition.

With this, the encoder can suppress an increase in the processing amountfor triangular partitions.

For example, the prediction image obtained when the partition isdetermined not to be a non-rectangular partition is the same as aportion corresponding to the partition, of a prediction image obtainedfor the image block without splitting the image block into the pluralityof partitions in a determined prediction mode. The determined predictionmode may be predetermined.

With this, the encoder can obtain a prediction image for a rectangularpartition in the same manner as in the case of obtaining a predictionimage for the image block without splitting the image block into aplurality of partitions. Accordingly, the encoder can simplify theprocessing.

For example, the circuitry obtains the second motion vector byperforming motion estimation using the first prediction image.

With this, the encoder can obtain an appropriate second motion vectorusing the first prediction image, and obtain an appropriate secondprediction image using the appropriate second motion vector.

For example, a decoder according to an aspect of the present disclosureis a decoder which includes circuitry and memory. Using the memory, thecircuitry splits an image block into a plurality of partitions, obtainsa prediction image for a partition included in the plurality ofpartitions, and decodes the image block using the prediction image. Inobtaining the prediction image, the circuitry: determines whether thepartition is a non-rectangular partition; when the partition isdetermined not to be a non-rectangular partition, obtains (i) a firstprediction image for the partition using a first motion vector for thepartition, (ii) a second motion vector for the partition using the firstprediction image, and (iii) a second prediction image for the partitionas the prediction image using the second motion vector; and when thepartition is determined to be a non-rectangular partition, obtains thefirst prediction image as the prediction image using the first motionvector, without using the second motion vector.

With this, the decoder can reduce the two-step operation fornon-rectangular partitions, and suppress an increase in the processingamount. Accordingly, the decoder can efficiently process the imageblock.

For example, the circuitry determines that the partition is anon-rectangular partition when the partition is a triangular partition.

With this, the decoder can suppress an increase in the processing amountfor triangular partitions.

For example, the prediction image obtained when the partition isdetermined not to be a non-rectangular partition is the same as aportion corresponding to the partition, of a prediction image obtainedfor the image block without splitting the image block into the pluralityof partitions in a determined prediction mode. The determined predictionmode may be predetermined.

With this, the decoder can obtain a prediction image for a rectangularpartition in the same manner as in the case of obtaining a predictionimage for the image block without splitting the image block into aplurality of partitions. Accordingly, the decoder can simplify theprocessing.

For example, the circuitry obtains the second motion vector byperforming motion estimation using the first prediction image.

With this, the decoder can obtain an appropriate second motion vectorusing the first prediction image, and obtain an appropriate secondprediction image using the appropriate second motion vector.

For example, an encoding method according to an aspect of the presentdisclosure is an encoding method which includes: splitting an imageblock into a plurality of partitions; obtaining a prediction image for apartition included in the plurality of partitions; and encoding theimage block using the prediction image. The obtaining of the predictionimage includes: determining whether the partition is a non-rectangularpartition; when the partition is determined not to be a non-rectangularpartition, obtaining (i) a first prediction image for the partitionusing a first motion vector for the partition, (ii) a second motionvector for the partition using the first prediction image, and (iii) asecond prediction image for the partition as the prediction image usingthe second motion vector; and when the partition is determined to be anon-rectangular partition, obtaining the first prediction image as theprediction image using the first motion vector, without using the secondmotion vector.

With this, it is possible to reduce the two-step operation fornon-rectangular partitions, and suppress an increase in the processingamount. Accordingly, the image block can be efficiently processed.

For example, a decoding method according to an aspect of the presentdisclosure is a decoding method which includes: splitting an image blockinto a plurality of partitions; obtaining a prediction image for apartition included in the plurality of partitions; and decoding theimage block using the prediction image. The obtaining of the predictionimage includes: determining whether the partition is a non-rectangularpartition; when the partition is determined not to be a non-rectangularpartition, obtaining (i) a first prediction image for the partitionusing a first motion vector for the partition, (ii) a second motionvector for the partition using the first prediction image, and (iii) asecond prediction image for the partition as the prediction image usingthe second motion vector; and when the partition is determined to be anon-rectangular partition, obtaining the first prediction image as theprediction image using the first motion vector, without using the secondmotion vector.

With this, it is possible to reduce the two-step operation fornon-rectangular partitions, and suppress an increase in the processingamount. Accordingly, the image block can be efficiently processed.

For example, an encoder according to an aspect of the present disclosureis an encoder which includes circuitry and memory. Using the memory, thecircuitry splits an image block into a plurality of partitions, obtainsa prediction image for a partition included in the plurality ofpartitions, and encodes the image block using the prediction image. Inobtaining the prediction image, the circuitry: determines whether thepartition is a non-rectangular partition; when the partition isdetermined not to be a non-rectangular partition, obtains (i) a firstprediction image for the partition, (ii) a gradient image for the firstprediction image, and (iii) a second prediction image as the predictionimage using the first prediction image and the gradient image; and whenthe partition is determined to be a non-rectangular partition, obtainsthe first prediction image as the prediction image without using thegradient image.

With this, the encoder can reduce use of a gradient image fornon-rectangular partitions, and suppress an increase in the processingamount. Accordingly, the encoder can efficiently process the imageblock.

For example, the circuitry determines that the partition is anon-rectangular partition when the partition is a triangular partition.

With this, the encoder can suppress an increase in the processing amountfor triangular partitions.

For example, the prediction image obtained when the partition isdetermined not to be a non-rectangular partition is the same as aportion corresponding to the partition, of a prediction image obtainedfor the image block without splitting the image block into the pluralityof partitions in a determined prediction mode. The determined predictionmode may be predetermined.

With this, the encoder can obtain a prediction image for a rectangularpartition in the same manner as in the case of obtaining a predictionimage for the image block without splitting the image block into aplurality of partitions. Accordingly, the encoder can simplify theprocessing.

For example, the circuitry obtains the gradient image by applying afilter to the first prediction image to extract a difference valuebetween pixels.

With this, the encoder can obtain an appropriate gradient image for thefirst prediction image, and obtain an appropriate second predictionimage using the appropriate gradient image.

For example, a decoder according to an aspect of the present disclosureis a decoder which includes circuitry and memory. Using the memory, thecircuitry splits an image block into a plurality of partitions, obtainsa prediction image for a partition included in the plurality ofpartitions, and decodes the image block using the prediction image. Inobtaining the prediction image, the circuitry: determines whether thepartition is a non-rectangular partition; when the partition isdetermined not to be a non-rectangular partition, obtains (i) a firstprediction image for the partition, (ii) a gradient image for the firstprediction image, and (iii) a second prediction image as the predictionimage using the first prediction image and the gradient image; and whenthe partition is determined to be a non-rectangular partition, obtainsthe first prediction image as the prediction image without using thegradient image.

With this, the decoder can reduce use of a gradient image fornon-rectangular partitions, and suppress an increase in the processingamount. Accordingly, the decoder can efficiently process the imageblock.

For example, the circuitry determines that the partition is anon-rectangular partition when the partition is a triangular partition.

With this, the decoder can suppress an increase in the processing amountfor triangular partitions.

For example, the prediction image obtained when the partition isdetermined not to be a non-rectangular partition is the same as aportion corresponding to the partition, of a prediction image obtainedfor the image block without splitting the image block into the pluralityof partitions in a determined prediction mode. The determined predictionmode may be predetermined.

With this, the decoder can obtain a prediction image for a rectangularpartition in the same manner as in the case of obtaining a predictionimage for the image block without splitting the image block into aplurality of partitions. Accordingly, the decoder can simplify theprocessing.

For example, the circuitry obtains the gradient image by applying afilter to the first prediction image to extract a difference valuebetween pixels.

With this, the decoder can obtain an appropriate gradient image for thefirst prediction image, and obtain an appropriate second predictionimage using the appropriate gradient image.

For example, an encoding method according to an aspect of the presentdisclosure is an encoding method which includes: splitting an imageblock into a plurality of partitions; obtaining a prediction image for apartition included in the plurality of partitions; and encoding theimage block using the prediction image. The obtaining of the predictionimage includes: determining whether the partition is a non-rectangularpartition; when the partition is determined not to be a non-rectangularpartition, obtaining (i) a first prediction image for the partition,(ii) a gradient image for the first prediction image, and (iii) a secondprediction image as the prediction image using the first predictionimage and the gradient image; and when the partition is determined to bea non-rectangular partition, obtaining the first prediction image as theprediction image without using the gradient image.

With this, it is possible to suppress an increase in the processingamount for non-rectangular partitions. Accordingly, the image block canbe efficiently processed.

For example, a decoding method according to an aspect of the presentdisclosure is a decoding method which includes: splitting an image blockinto a plurality of partitions; obtaining a prediction image for apartition included in the plurality of partitions; and decoding theimage block using the prediction image. The obtaining of the predictionimage includes: determining whether the partition is a non-rectangularpartition; when the partition is determined not to be a non-rectangularpartition, obtaining (i) a first prediction image for the partition,(ii) a gradient image for the first prediction image, and (iii) a secondprediction image as the prediction image using the first predictionimage and the gradient image; and when the partition is determined to bea non-rectangular partition, obtaining the first prediction image as theprediction image without using the gradient image.

With this, it is possible to suppress an increase in the processingamount for non-rectangular partitions. Accordingly, the image block canbe efficiently processed.

For example, an encoder according to an aspect of the present disclosureis an encoder which includes circuitry and memory. Using the memory, thecircuitry: splits an image block into a plurality of partitions;generates a motion vector candidate list for a partition included in theplurality of partitions; obtains a motion vector for the partition fromthe motion vector candidate list; performs inter prediction processingfor the partition using the motion vector for the partition; and encodesthe image block using a result of the inter prediction processing. Ingenerating the motion vector candidate list, the circuitry: determineswhether the partition is a non-rectangular partition; when the partitionis determined not to be a non-rectangular partition, generates themotion vector candidate list using at least one motion vector among aplurality of motion vectors for a plurality of spatially neighboringpartitions that spatially neighbor the partition, a plurality of motionvectors for a plurality of temporally neighboring partitions thattemporally neighbor the partition, and a plurality of motion vectors fora plurality of sub-partitions included in the partition; and when thepartition is determined to be a non-rectangular partition, generates themotion vector candidate list using at least one motion vector among theplurality of motion vectors for the plurality of spatially neighboringpartitions and the plurality of motion vectors for the plurality oftemporally neighboring partitions, without using the plurality of motionvectors for the plurality of sub-partitions.

With this, the encoder can reduce, for non-rectangular partitions, useof a plurality of motion vectors for a plurality of sub-partitions, andsuppress an increase in the processing amount. Accordingly, the encodercan efficiently process the image block.

For example, the circuitry determines that the partition is anon-rectangular partition when the partition is a triangular partition.

With this, the encoder can suppress an increase in the processing amountfor triangular partitions.

For example, the plurality of motion vectors for the plurality ofsub-partitions include motion vectors predicted from motion vectors forregions which spatially or temporally neighbor the plurality ofsub-partitions.

With this, the encoder can use a motion vector which is predicted, as amotion vector for a sub-partition, from a motion vector for a regionneighboring the sub-partition.

For example, the motion vector candidate list generated when thepartition is determined not to be a non-rectangular partition is thesame as a motion vector candidate list generated for the image block ina determined prediction mode. The determined prediction mode may bepredetermined.

With this, the encoder can generate the motion vector candidate list fora rectangular partition in the same manner as in the case of generatinga motion vector candidate list for the image block. Accordingly, theencoder can simplify the processing.

For example, each of the plurality of temporally neighboring partitionsis a co-located partition which, in a picture different from a picturethat includes the partition, is located in a position that correspondsto a position of the partition.

With this, the encoder can use the motion vector for the co-locatedpartition as a motion vector for the temporally neighboring partition.

For example, a decoder according to an aspect of the present disclosureis a decoder which includes circuitry and memory. Using the memory, thecircuitry: splits an image block into a plurality of partitions;generates a motion vector candidate list for a partition included in theplurality of partitions; obtains a motion vector for the partition fromthe motion vector candidate list; performs inter prediction processingfor the partition using the motion vector for the partition; and decodesthe image block using a result of the inter prediction processing. Ingenerating the motion vector candidate list, the circuitry: determineswhether the partition is a non-rectangular partition; when the partitionis determined not to be a non-rectangular partition, generates themotion vector candidate list using at least one motion vector among aplurality of motion vectors for a plurality of spatially neighboringpartitions that spatially neighbor the partition, a plurality of motionvectors for a plurality of temporally neighboring partitions thattemporally neighbor the partition, and a plurality of motion vectors fora plurality of sub-partitions included in the partition; and when thepartition is determined to be a non-rectangular partition, generates themotion vector candidate list using at least one motion vector among theplurality of motion vectors for the plurality of spatially neighboringpartitions and the plurality of motion vectors for the plurality oftemporally neighboring partitions, without using the plurality of motionvectors for the plurality of sub-partitions.

With this, the decoder can reduce, for non-rectangular partitions, useof a plurality of motion vectors for a plurality of sub-partitions, andsuppress an increase in the processing amount. Accordingly, the decodercan efficiently process the image block.

For example, the circuitry determines that the partition is anon-rectangular partition when the partition is a triangular partition.

With this, the decoder can suppress an increase in the processing amountfor triangular partitions.

For example, the plurality of motion vectors for the plurality ofsub-partitions include motion vectors predicted from motion vectors forregions which spatially or temporally neighbor the plurality ofsub-partitions.

With this, the decoder can use a motion vector which is predicted, as amotion vector for a sub-partition, from a motion vector for a regionneighboring the sub-partition.

For example, the motion vector candidate list generated when thepartition is determined not to be a non-rectangular partition is thesame as a motion vector candidate list generated for the image block ina determined prediction mode. The determined prediction mode may bepredetermined.

With this, the decoder can generate the motion vector candidate list fora rectangular partition in the same manner as in the case of generatinga motion vector candidate list for the image block. Accordingly, thedecoder can simplify the processing.

For example, each of the plurality of temporally neighboring partitionsis a co-located partition which, in a picture different from a picturethat includes the partition, is located in a position that correspondsto a position of the partition.

With this, the decoder can use the motion vector for the co-locatedpartition as a motion vector for the temporally neighboring partition.

For example, an encoding method according to an aspect of the presentdisclosure is an encoding method which includes: splitting an imageblock into a plurality of partitions; generating a motion vectorcandidate list for a partition included in the plurality of partitions;obtaining a motion vector for the partition from the motion vectorcandidate list; performing inter prediction processing for the partitionusing the motion vector for the partition; and encoding the image blockusing a result of the inter prediction processing. The generating of themotion vector candidate list includes: determining whether the partitionis a non-rectangular partition; when the partition is determined not tobe a non-rectangular partition, generating the motion vector candidatelist using at least one motion vector among a plurality of motionvectors for a plurality of spatially neighboring partitions thatspatially neighbor the partition, a plurality of motion vectors for aplurality of temporally neighboring partitions that temporally neighborthe partition, and a plurality of motion vectors for a plurality ofsub-partitions included in the partition; and when the partition isdetermined to be a non-rectangular partition, generating the motionvector candidate list using at least one motion vector among theplurality of motion vectors for the plurality of spatially neighboringpartitions and the plurality of motion vectors for the plurality oftemporally neighboring partitions, without using the plurality of motionvectors for the plurality of sub-partitions.

With this, it is possible to reduce, for non-rectangular partitions, useof a plurality of motion vectors for a plurality of sub-partitions, andsuppress an increase in the processing amount. Accordingly, the imageblock can be efficiently processed.

For example, a decoding method according to an aspect of the presentdisclosure is a decoding method which includes: splitting an image blockinto a plurality of partitions; generating a motion vector candidatelist for a partition included in the plurality of partitions; obtaininga motion vector for the partition from the motion vector candidate list;performing inter prediction processing for the partition using themotion vector for the partition; and decoding the image block using aresult of the inter prediction processing. The generating of the motionvector candidate list includes: determining whether the partition is anon-rectangular partition; when the partition is determined not to be anon-rectangular partition, generating the motion vector candidate listusing at least one motion vector among a plurality of motion vectors fora plurality of spatially neighboring partitions that spatially neighborthe partition, a plurality of motion vectors for a plurality oftemporally neighboring partitions that temporally neighbor thepartition, and a plurality of motion vectors for a plurality ofsub-partitions included in the partition; and when the partition isdetermined to be a non-rectangular partition, generating the motionvector candidate list using at least one motion vector among theplurality of motion vectors for the plurality of spatially neighboringpartitions and the plurality of motion vectors for the plurality oftemporally neighboring partitions, without using the plurality of motionvectors for the plurality of sub-partitions.

With this, it is possible to reduce, for non-rectangular partitions, useof a plurality of motion vectors for a plurality of sub-partitions, andsuppress an increase in the processing amount. Accordingly, the imageblock can be efficiently processed.

Moreover, for example, the encoder according to an aspect of the presentdisclosure includes a splitter, an intra predictor, an inter predictor,a transformer, a quantizer, an entropy encoder, and a loop filter. Thesplitter splits a picture into a plurality of image blocks. The intrapredictor performs intra prediction on an image block included in theplurality of image blocks. The inter predictor performs inter predictionon the image block. The transformer generates transform coefficients bytransforming prediction errors between an original image and aprediction image obtained through the intra prediction or the interprediction. The quantizer generates quantized coefficients by quantizingthe transform coefficients. The entropy encoder generates an encodedbitstream by encoding the quantized coefficients. The loop filterapplies a filter to a reconstructed image generated using the predictionimage.

For example, the entropy encoder encodes the image block. In encodingthe image block, the entropy encoder: obtains one or more sizeparameters related to the size of the image block; determines whetherthe one or more size parameters and one or more thresholds satisfy adetermined relationship; encodes a split parameter when the one or moresize parameters and the one or more thresholds are determined to satisfythe determined relationship, the split parameter indicating whether theimage block is to be split into a plurality of partitions including anon-rectangular partition; and encodes the image block after splittingthe image block into the plurality of partitions when the splitparameter indicates that the image block is to be split into theplurality of partitions. The determined relationship may bepredetermined.

For example, the inter predictor splits the image block into a pluralityof partitions, and obtains a prediction image for a partition includedin the plurality of partitions. In obtaining the prediction image, theinter predictor: determines whether the partition is a non-rectangularpartition; when the partition is determined not to be a non-rectangularpartition, obtains (i) a first prediction image for the partition usinga first motion vector for the partition, (ii) a second motion vector forthe partition using the first prediction image, and (iii) a secondprediction image for the partition as the prediction image using thesecond motion vector; and when the partition is determined to be anon-rectangular partition, obtains the first prediction image as theprediction image using the first motion vector, without using the secondmotion vector.

For example, the inter predictor splits the image block into a pluralityof partitions, and obtains a prediction image for a partition includedin the plurality of partitions. In obtaining the prediction image, theinter predictor: determines whether the partition is a non-rectangularpartition; when the partition is determined not to be a non-rectangularpartition, obtains (i) a first prediction image for the partition, (ii)a gradient image for the first prediction image, and (iii) a secondprediction image as the prediction image using the first predictionimage and the gradient image; and when the partition is determined to bea non-rectangular partition, obtains the first prediction image as theprediction image without using the gradient image.

For example, the inter predictor: splits the image block into aplurality of partitions; generates a motion vector candidate list for apartition included in the plurality of partitions; obtains a motionvector for the partition from the motion vector candidate list; andperforms inter prediction processing for the partition using the motionvector for the partition. In generating the motion vector candidatelist, the inter predictor: determines whether the partition is anon-rectangular partition; when the partition is determined not to be anon-rectangular partition, generates the motion vector candidate listusing at least one motion vector among a plurality of motion vectors fora plurality of spatially neighboring partitions that spatially neighborthe partition, a plurality of motion vectors for a plurality oftemporally neighboring partitions that temporally neighbor thepartition, and a plurality of motion vectors for a plurality ofsub-partitions included in the partition; and when the partition isdetermined to be a non-rectangular partition, generates the motionvector candidate list using at least one motion vector among theplurality of motion vectors for the plurality of spatially neighboringpartitions and the plurality of motion vectors for the plurality oftemporally neighboring partitions, without using the plurality of motionvectors for the plurality of sub-partitions.

Moreover, for example, the decoder according to an aspect of the presentdisclosure includes an entropy decoder, an inverse quantizer, an inversetransformer, an intra predictor, an inter predictor, and a loop filter.The entropy decoder decodes quantized coefficients of a partition in apicture, from an encoded bitstream. The inverse quantizerinverse-quantizes the quantized coefficients to obtain transformcoefficients. The inverse transformer inverse-transforms the transformcoefficients to obtain a prediction error. The intra predictor performsintra prediction on the partition. The inter predictor performs interprediction on the partition. The loop filter applies a filter to areconstructed image generated using the prediction image obtainedthrough the intra prediction or the inter prediction and the predictionerror.

For example, the entropy decoder decodes the image block using thememory. In decoding the image block, the entropy decoder: obtains one ormore size parameters related to a size of the image block; determineswhether the one or more size parameters and one or more thresholdssatisfy a determined relationship; decodes a split parameter when theone or more size parameters and the one or more thresholds aredetermined to satisfy the determined relationship, the split parameterindicating whether the image block is to be split into a plurality ofpartitions including a non-rectangular partition; and decodes the imageblock after splitting the image block into the plurality of partitionswhen the split parameter indicates that the image block is to be splitinto the plurality of partitions. The determined relationship may bepredetermined.

For example, the inter predictor splits the image block into a pluralityof partitions, and obtains a prediction image for a partition includedin the plurality of partitions. In obtaining the prediction image, theinter predictor: determines whether the partition is a non-rectangularpartition; when the partition is determined not to be a non-rectangularpartition, obtains (i) a first prediction image for the partition usinga first motion vector for the partition, (ii) a second motion vector forthe partition using the first prediction image, and (iii) a secondprediction image for the partition as the prediction image using thesecond motion vector; and when the partition is determined to be anon-rectangular partition, obtains the first prediction image as theprediction image using the first motion vector, without using the secondmotion vector.

For example, the inter predictor splits the image block into a pluralityof partitions, and obtains a prediction image for a partition includedin the plurality of partitions. In obtaining the prediction image, theinter predictor: determines whether the partition is a non-rectangularpartition; when the partition is determined not to be a non-rectangularpartition, obtains (i) a first prediction image for the partition, (ii)a gradient image for the first prediction image, and (iii) a secondprediction image as the prediction image using the first predictionimage and the gradient image; and when the partition is determined to bea non-rectangular partition, obtains the first prediction image as theprediction image without using the gradient image.

For example, the inter predictor splits the image block into a pluralityof partitions; generates a motion vector candidate list for a partitionincluded in the plurality of partitions; obtains a motion vector for thepartition from the motion vector candidate list; and performs interprediction processing for the partition using the motion vector for thepartition. In generating the motion vector candidate list, the interpredictor: determines whether the partition is a non-rectangularpartition; when the partition is determined not to be a non-rectangularpartition, generates the motion vector candidate list using at least onemotion vector among a plurality of motion vectors for a plurality ofspatially neighboring partitions that spatially neighbor the partition,a plurality of motion vectors for a plurality of temporally neighboringpartitions that temporally neighbor the partition, and a plurality ofmotion vectors for a plurality of sub-partitions included in thepartition; and when the partition is determined to be a non-rectangularpartition, generates the motion vector candidate list using at least onemotion vector among the plurality of motion vectors for the plurality ofspatially neighboring partitions and the plurality of motion vectors forthe plurality of temporally neighboring partitions, without using theplurality of motion vectors for the plurality of sub-partitions.

Note that these general or specific aspects may be implemented by asystem, a device, a method, an integrated circuit, a computer program,or a non-transitory computer-readable recording medium such as a CD-ROM,or by any combination of systems, devices, methods, integrated circuits,computer programs, or recording media.

Hereinafter, embodiments will be described with reference to thedrawings.

Note that the embodiments described below each show a general orspecific example. The numerical values, shapes, materials, components,the arrangement and connection of the components, steps, order of thesteps, etc., indicated in the following embodiments are mere examples,and therefore are not intended to limit the scope of the claims.Therefore, among the components in the following embodiments, those notrecited in any of the independent claims defining the broadest inventiveconcepts are described as optional components.

Embodiment 1

First, an outline of Embodiment 1 will be presented. Embodiment 1 is oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in subsequent description of aspects of thepresent disclosure are applicable. Note that Embodiment 1 is merely oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in the description of aspects of the presentdisclosure are applicable. The processes and/or configurations presentedin the description of aspects of the present disclosure can also beimplemented in an encoder and a decoder different from those accordingto Embodiment 1.

When the processes and/or configurations presented in the description ofaspects of the present disclosure are applied to Embodiment 1, forexample, any of the following may be performed.

(1) regarding the encoder or the decoder according to Embodiment 1,among components included in the encoder or the decoder according toEmbodiment 1, substituting a component corresponding to a componentpresented in the description of aspects of the present disclosure with acomponent presented in the description of aspects of the presentdisclosure;

(2) regarding the encoder or the decoder according to Embodiment 1,implementing discretionary changes to functions or implemented processesperformed by one or more components included in the encoder or thedecoder according to Embodiment 1, such as addition, substitution, orremoval, etc., of such functions or implemented processes, thensubstituting a component corresponding to a component presented in thedescription of aspects of the present disclosure with a componentpresented in the description of aspects of the present disclosure;

(3) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, implementing discretionary changes such asaddition of processes and/or substitution, removal of one or more of theprocesses included in the method, and then substituting a processescorresponding to a process presented in the description of aspects ofthe present disclosure with a process presented in the description ofaspects of the present disclosure;

(4) combining one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(5) combining a component including one or more functions included inone or more components included in the encoder or the decoder accordingto Embodiment 1, or a component that implements one or more processesimplemented by one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(6) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, among processes included in the method,substituting a process corresponding to a process presented in thedescription of aspects of the present disclosure with a processpresented in the description of aspects of the present disclosure; and

(7) combining one or more processes included in the method implementedby the encoder or the decoder according to Embodiment 1 with a processpresented in the description of aspects of the present disclosure.

Note that the implementation of the processes and/or configurationspresented in the description of aspects of the present disclosure is notlimited to the above examples. For example, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be implemented in a device used for a purpose differentfrom the moving picture/picture encoder or the moving picture/picturedecoder disclosed in Embodiment 1. Moreover, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be independently implemented. Moreover, processes and/orconfigurations described in different aspects may be combined.

[Encoder Outline]

First, the encoder according to Embodiment 1 will be outlined. FIG. 1 isa block diagram illustrating a functional configuration of encoder 100according to Embodiment 1. Encoder 100 is a moving picture/pictureencoder that encodes a moving picture/picture block by block.

As illustrated in FIG. 1, encoder 100 is a device that encodes a pictureblock by block, and includes splitter 102, subtractor 104, transformer106, quantizer 108, entropy encoder 110, inverse quantizer 112, inversetransformer 114, adder 116, block memory 118, loop filter 120, framememory 122, intra predictor 124, inter predictor 126, and predictioncontroller 128.

Encoder 100 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.Alternatively, encoder 100 may be realized as one or more dedicatedelectronic circuits corresponding to splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, loop filter 120, intrapredictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, each component included in encoder 100 will be described.

[Splitter]

Splitter 102 splits each picture included in an input moving pictureinto blocks, and outputs each block to subtractor 104. For example,splitter 102 first splits a picture into blocks of a fixed size (forexample, 128×128). The fixed size block is also referred to as codingtree unit (CTU). Splitter 102 then splits each fixed size block intoblocks of variable sizes (for example, 64×64 or smaller), based onrecursive quadtree and/or binary tree block splitting. The variable sizeblock is also referred to as a coding unit (CU), a prediction unit (PU),or a transform unit (TU). Note that in this embodiment, there is no needto differentiate between CU, PU, and TU; all or some of the blocks in apicture may be processed per CU, PU, or TU.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1. In FIG. 2, the solid lines represent block boundaries ofblocks split by quadtree block splitting, and the dashed lines representblock boundaries of blocks split by binary tree block splitting.

Here, block 10 is a square 128×128 pixel block (128×128 block). This128×128 block 10 is first split into four square 64×64 blocks (quadtreeblock splitting).

The top left 64×64 block is further vertically split into two rectangle32×64 blocks, and the left 32×64 block is further vertically split intotwo rectangle 16×64 blocks (binary tree block splitting). As a result,the top left 64×64 block is split into two 16×64 blocks 11 and 12 andone 32×64 block 13.

The top right 64×64 block is horizontally split into two rectangle 64×32blocks 14 and 15 (binary tree block splitting).

The bottom left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The top left block and the bottom rightblock among the four 32×32 blocks are further split. The top left 32×32block is vertically split into two rectangle 16×32 blocks, and the right16×32 block is further horizontally split into two 16×16 blocks (binarytree block splitting). The bottom right 32×32 block is horizontallysplit into two 32×16 blocks (binary tree block splitting). As a result,the bottom left 64×64 block is split into 16×32 block 16, two 16×16blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16 blocks 21and 22.

The bottom right 64×64 block 23 is not split.

As described above, in FIG. 2, block 10 is split into 13 variable sizeblocks 11 through 23 based on recursive quadtree and binary tree blocksplitting. This type of splitting is also referred to as quadtree plusbinary tree (QTBT) splitting.

Note that in FIG. 2, one block is split into four or two blocks(quadtree or binary tree block splitting), but splitting is not limitedto this example. For example, one block may be split into three blocks(ternary block splitting). Splitting including such ternary blocksplitting is also referred to as multi-type tree (MBT) splitting.

[Subtractor]

Subtractor 104 subtracts a prediction signal (prediction sample) from anoriginal signal (original sample) per block split by splitter 102. Inother words, subtractor 104 calculates prediction errors (also referredto as residuals) of a block to be encoded (hereinafter referred to as acurrent block). Subtractor 104 then outputs the calculated predictionerrors to transformer 106.

The original signal is a signal input into encoder 100, and is a signalrepresenting an image for each picture included in a moving picture (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

[Transformer]

Transformer 106 transforms spatial domain prediction errors intofrequency domain transform coefficients, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a defined discrete cosine transform (DCT) ordiscrete sine transform (DST) to spatial domain prediction errors. Thedefined transform may be predefined.

Note that transformer 106 may adaptively select a transform type fromamong a plurality of transform types, and transform prediction errorsinto transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V, DCT-VIII,DST-I, and DST-VII. FIG. 3 is a chart indicating transform basisfunctions for each transform type. In FIG. 3, N indicates the number ofinput pixels. For example, selection of a transform type from among theplurality of transform types may depend on the prediction type (intraprediction and inter prediction), and may depend on intra predictionmode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an AMT flag) and information indicating the selectedtransform type is signalled at the CU level. Note that the signaling ofsuch information need not be performed at the CU level, and may beperformed at another level (for example, at the sequence level, picturelevel, slice level, tile level, or CTU level).

Moreover, transformer 106 may apply a secondary transform to thetransform coefficients (transform result). Such a secondary transform isalso referred to as adaptive secondary transform (AST) or non-separablesecondary transform (NSST). For example, transformer 106 applies asecondary transform to each sub-block (for example, each 4×4 sub-block)included in the block of the transform coefficients corresponding to theintra prediction errors. Information indicating whether to apply NSSTand information related to the transform matrix used in NSST aresignalled at the CU level. Note that the signaling of such informationneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, or CTU level).

Here, a separable transform is a method in which a transform isperformed a plurality of times by separately performing a transform foreach direction according to the number of dimensions input. Anon-separable transform is a method of performing a collective transformin which two or more dimensions in a multidimensional input arecollectively regarded as a single dimension.

In one example of a non-separable transform, when the input is a 4×4block, the 4×4 block is regarded as a single array including 16components, and the transform applies a 16×16 transform matrix to thearray.

Moreover, similar to above, after an input 4×4 block is regarded as asingle array including 16 components, a transform that performs aplurality of Givens rotations on the array (i.e., a Hypercube-GivensTransform) is also one example of a non-separable transform.

[Quantizer]

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in a determinedscanning order, the transform coefficients of the current block, andquantizes the scanned transform coefficients based on quantizationparameters (QP) corresponding to the transform coefficients. Quantizer108 then outputs the quantized transform coefficients (hereinafterreferred to as quantized coefficients) of the current block to entropyencoder 110 and inverse quantizer 112. The determined scanning order maybe predetermined.

A determined order is an order for quantizing/inverse quantizingtransform coefficients. For example, a determined scanning order isdefined as ascending order of frequency (from low to high frequency) ordescending order of frequency (from high to low frequency).

A quantization parameter is a parameter defining a quantization stepsize (quantization width). For example, if the value of the quantizationparameter increases, the quantization step size also increases. In otherwords, if the value of the quantization parameter increases, thequantization error increases.

[Entropy Encoder]

Entropy encoder 110 generates an encoded signal (encoded bitstream) byvariable length encoding quantized coefficients, which are inputs fromquantizer 108. More specifically, entropy encoder 110, for example,binarizes quantized coefficients and arithmetic encodes the binarysignal.

[Inverse Quantizer]

Inverse quantizer 112 inverse quantizes quantized coefficients, whichare inputs from quantizer 108. More specifically, inverse quantizer 112inverse quantizes, in a determined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114. The determined scanning order may bepredetermined.

[Inverse Transformer]

Inverse transformer 114 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 112. More specifically, inverse transformer 114 restores theprediction errors of the current block by applying an inverse transformcorresponding to the transform applied by transformer 106 on thetransform coefficients. Inverse transformer 114 then outputs therestored prediction errors to adder 116.

Note that since information is lost in quantization, the restoredprediction errors do not match the prediction errors calculated bysubtractor 104. In other words, the restored prediction errors includequantization errors.

[Adder]

Adder 116 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 114, and prediction samples,which are inputs from prediction controller 128. Adder 116 then outputsthe reconstructed block to block memory 118 and loop filter 120. Areconstructed block is also referred to as a local decoded block.

[Block Memory]

Block memory 118 is storage for storing blocks in a picture to beencoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 118 storesreconstructed blocks output from adder 116.

[Loop Filter]

Loop filter 120 applies a loop filter to blocks reconstructed by adder116, and outputs the filtered reconstructed blocks to frame memory 122.A loop filter is a filter used in an encoding loop (in-loop filter), andincludes, for example, a deblocking filter (DF), a sample adaptiveoffset (SAO), and an adaptive loop filter (ALF).

In ALF, a least square error filter for removing compression artifactsis applied. For example, one filter from among a plurality of filters isselected for each 2×2 sub-block in the current block based on directionand activity of local gradients, and is applied.

More specifically, first, each sub-block (for example, each 2×2sub-block) is categorized into one out of a plurality of classes (forexample, 15 or 25 classes). The classification of the sub-block is basedon gradient directionality and activity. For example, classificationindex C is derived based on gradient directionality D (for example, 0 to2 or 0 to 4) and gradient activity A (for example, 0 to 4) (for example,C=5D+A). Then, based on classification index C, each sub-block iscategorized into one out of a plurality of classes (for example, 15 or25 classes).

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by summing gradients of a plurality ofdirections and quantizing the sum.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in ALF is, for example, a circular symmetricfilter shape. FIG. 4A through FIG. 4C illustrate examples of filtershapes used in ALF. FIG. 4A illustrates a 5×5 diamond shape filter, FIG.4B illustrates a 7×7 diamond shape filter, and FIG. 4C illustrates a 9×9diamond shape filter. Information indicating the filter shape issignalled at the picture level. Note that the signaling of informationindicating the filter shape need not be performed at the picture level,and may be performed at another level (for example, at the sequencelevel, slice level, tile level, CTU level, or CU level).

The enabling or disabling of ALF is determined at the picture level orCU level. For example, for luma, the decision to apply ALF or not isdone at the CU level, and for chroma, the decision to apply ALF or notis done at the picture level. Information indicating whether ALF isenabled or disabled is signalled at the picture level or CU level. Notethat the signaling of information indicating whether ALF is enabled ordisabled need not be performed at the picture level or CU level, and maybe performed at another level (for example, at the sequence level, slicelevel, tile level, or CTU level).

The coefficients set for the plurality of selectable filters (forexample, 15 or 25 filters) is signalled at the picture level. Note thatthe signaling of the coefficients set need not be performed at thepicture level, and may be performed at another level (for example, atthe sequence level, slice level, tile level, CTU level, CU level, orsub-block level).

[Frame Memory]

Frame memory 122 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 122 stores reconstructed blocks filtered byloop filter 120.

[Intra Predictor]

Intra predictor 124 generates a prediction signal (intra predictionsignal) by intra predicting the current block with reference to a blockor blocks in the current picture and stored in block memory 118 (alsoreferred to as intra frame prediction). More specifically, intrapredictor 124 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of predefined intra prediction modes. Theintra prediction modes include one or more non-directional predictionmodes and a plurality of directional prediction modes.

The one or more non-directional prediction modes include, for example,planar prediction mode and DC prediction mode defined in theH.265/high-efficiency video coding (HEVC) standard (see NPL 1).

The plurality of directional prediction modes include, for example, the33 directional prediction modes defined in the H.265/HEVC standard. Notethat the plurality of directional prediction modes may further include32 directional prediction modes in addition to the 33 directionalprediction modes (for a total of 65 directional prediction modes). FIG.5A illustrates 67 intra prediction modes used in intra prediction (twonon-directional prediction modes and 65 directional prediction modes).The solid arrows represent the 33 directions defined in the H.265/HEVCstandard, and the dashed arrows represent the additional 32 directions.

Note that a luma block may be referenced in chroma block intraprediction. In other words, a chroma component of the current block maybe predicted based on a luma component of the current block. Such intraprediction is also referred to as cross-component linear model (CCLM)prediction. Such a chroma block intra prediction mode that references aluma block (referred to as, for example, CCLM mode) may be added as oneof the chroma block intra prediction modes.

Intra predictor 124 may correct post-intra-prediction pixel values basedon horizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC or not (referred to as, for example, a PDPC flag)is, for example, signalled at the CU level. Note that the signaling ofthis information need not be performed at the CU level, and may beperformed at another level (for example, on the sequence level, picturelevel, slice level, tile level, or CTU level).

[Inter Predictor]

Inter predictor 126 generates a prediction signal (inter predictionsignal) by inter predicting the current block with reference to a blockor blocks in a reference picture, which is different from the currentpicture and is stored in frame memory 122 (also referred to as interframe prediction). Inter prediction is performed per current block orper sub-block (for example, per 4×4 block) in the current block. Forexample, inter predictor 126 performs motion estimation in a referencepicture for the current block or sub-block. Inter predictor 126 thengenerates an inter prediction signal of the current block or sub-blockby motion compensation by using motion information (for example, amotion vector) obtained from motion estimation. Inter predictor 126 thenoutputs the generated inter prediction signal to prediction controller128.

The motion information used in motion compensation is signalled. Amotion vector predictor may be used for the signaling of the motionvector. In other words, the difference between the motion vector and themotion vector predictor may be signalled.

Note that the inter prediction signal may be generated using motioninformation for a neighboring block in addition to motion informationfor the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated per sub-blockin the current block by calculating a weighted sum of a predictionsignal based on motion information obtained from motion estimation and aprediction signal based on motion information for a neighboring block.Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In such an OBMC mode, information indicating sub-block size for OBMC(referred to as, for example, OBMC block size) is signalled at thesequence level. Moreover, information indicating whether to apply theOBMC mode or not (referred to as, for example, an OBMC flag) issignalled at the CU level. Note that the signaling of such informationneed not be performed at the sequence level and CU level, and may beperformed at another level (for example, at the picture level, slicelevel, tile level, CTU level, or sub-block level).

Hereinafter, the OBMC mode will be described in further detail. FIG. 5Bis a flowchart and FIG. 5C is a conceptual diagram for illustrating anoutline of a prediction image correction process performed via OBMCprocessing.

First, a prediction image (Pred) is obtained through typical motioncompensation using a motion vector (MV) assigned to the current block.

Next, a prediction image (Pred_L) is obtained by applying a motionvector (MV L) of the encoded neighboring left block to the currentblock, and a first pass of the correction of the prediction image ismade by superimposing the prediction image and Pred_L.

Similarly, a prediction image (Pred_U) is obtained by applying a motionvector (MV U) of the encoded neighboring upper block to the currentblock, and a second pass of the correction of the prediction image ismade by superimposing the prediction image resulting from the first passand Pred_U. The result of the second pass is the final prediction image.

Note that the above example is of a two-pass correction method using theneighboring left and upper blocks, but the method may be a three-pass orhigher correction method that also uses the neighboring right and/orlower block.

Note that the region subject to superimposition may be the entire pixelregion of the block, and, alternatively, may be a partial block boundaryregion.

Note that here, the prediction image correction process is described asbeing based on a single reference picture, but the same applies when aprediction image is corrected based on a plurality of referencepictures. In such a case, after corrected prediction images resultingfrom performing correction based on each of the reference pictures areobtained, the obtained corrected prediction images are furthersuperimposed to obtain the final prediction image.

Note that the unit of the current block may be a prediction block and,alternatively, may be a sub-block obtained by further dividing theprediction block.

One example of a method for determining whether to implement OBMCprocessing is by using an obmc_flag, which is a signal that indicateswhether to implement OBMC processing. As one specific example, theencoder determines whether the current block belongs to a regionincluding complicated motion. The encoder sets the obmc_flag to a valueof “1” when the block belongs to a region including complicated motionand implements OBMC processing when encoding, and sets the obmc_flag toa value of “0” when the block does not belong to a region includingcomplication motion and encodes without implementing OBMC processing.The decoder switches between implementing OBMC processing or not bydecoding the obmc_flag written in the stream and performing the decodingin accordance with the flag value.

Note that the motion information may be derived on the decoder sidewithout being signalled. For example, a merge mode defined in theH.265/HEVC standard may be used. Moreover, for example, the motioninformation may be derived by performing motion estimation on thedecoder side. In this case, motion estimation is performed without usingthe pixel values of the current block.

Here, a mode for performing motion estimation on the decoder side willbe described. A mode for performing motion estimation on the decoderside is also referred to as pattern matched motion vector derivation(PMMVD) mode or frame rate up-conversion (FRUC) mode.

One example of FRUC processing is illustrated in FIG. 5D. First, acandidate list (a candidate list may be a merge list) of candidates eachincluding a motion vector predictor is generated with reference tomotion vectors of encoded blocks that spatially or temporally neighborthe current block. Next, the best candidate MV is selected from among aplurality of candidate MVs registered in the candidate list. Forexample, evaluation values for the candidates included in the candidatelist are calculated and one candidate is selected based on thecalculated evaluation values.

Next, a motion vector for the current block is derived from the motionvector of the selected candidate. More specifically, for example, themotion vector for the current block is calculated as the motion vectorof the selected candidate (best candidate MV), as-is. Alternatively, themotion vector for the current block may be derived by pattern matchingperformed in the vicinity of a position in a reference picturecorresponding to the motion vector of the selected candidate. In otherwords, when the vicinity of the best candidate MV is searched via thesame method and an MV having a better evaluation value is found, thebest candidate MV may be updated to the MV having the better evaluationvalue, and the MV having the better evaluation value may be used as thefinal MV for the current block. Note that a configuration in which thisprocessing is not implemented is also acceptable.

The same processes may be performed in cases in which the processing isperformed in units of sub-blocks.

Note that an evaluation value is calculated by calculating thedifference in the reconstructed image by pattern matching performedbetween a region in a reference picture corresponding to a motion vectorand a determined region. Note that the evaluation value may becalculated by using some other information in addition to thedifference. The determined region may be predetermined.

The pattern matching used is either first pattern matching or secondpattern matching. First pattern matching and second pattern matching arealso referred to as bilateral matching and template matching,respectively.

In the first pattern matching, pattern matching is performed between twoblocks along the motion trajectory of the current block in two differentreference pictures. Therefore, in the first pattern matching, a regionin another reference picture conforming to the motion trajectory of thecurrent block is used as the determined region for the above-describedcalculation of the candidate evaluation value.

FIG. 6 is for illustrating one example of pattern matching (bilateralmatching) between two blocks along a motion trajectory. As illustratedin FIG. 6, in the first pattern matching, two motion vectors (MV0, MV1)are derived by finding the best match between two blocks along themotion trajectory of the current block (Cur block) in two differentreference pictures (Ref0, Ref1). More specifically, a difference between(i) a reconstructed image in a specified position in a first encodedreference picture (Ref0) specified by a candidate MV and (ii) areconstructed picture in a specified position in a second encodedreference picture (Ref1) specified by a symmetrical MV scaled at adisplay time interval of the candidate MV may be derived, and theevaluation value for the current block may be calculated by using thederived difference. The candidate MV having the best evaluation valueamong the plurality of candidate MVs may be selected as the final MV.

Under the assumption of continuous motion trajectory, the motion vectors(MV0, MV1) pointing to the two reference blocks shall be proportional tothe temporal distances (TD0, TD1) between the current picture (Cur Pic)and the two reference pictures (Ref0, Ref1). For example, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture to the two reference picturesis the same, the first pattern matching derives a mirror basedbi-directional motion vector.

In the second pattern matching, pattern matching is performed between atemplate in the current picture (blocks neighboring the current block inthe current picture (for example, the top and/or left neighboringblocks)) and a block in a reference picture. Therefore, in the secondpattern matching, a block neighboring the current block in the currentpicture is used as the determined region for the above-describedcalculation of the candidate evaluation value.

FIG. 7 is for illustrating one example of pattern matching (templatematching) between a template in the current picture and a block in areference picture. As illustrated in FIG. 7, in the second patternmatching, a motion vector of the current block is derived by searching areference picture (Ref0) to find the block that best matches neighboringblocks of the current block (Cur block) in the current picture (CurPic). More specifically, a difference between (i) a reconstructed imageof an encoded region that is both or one of the neighboring left andneighboring upper region and (ii) a reconstructed picture in the sameposition in an encoded reference picture (Ref0) specified by a candidateMV may be derived, and the evaluation value for the current block may becalculated by using the derived difference. The candidate MV having thebest evaluation value among the plurality of candidate MVs may beselected as the best candidate MV.

Information indicating whether to apply the FRUC mode or not (referredto as, for example, a FRUC flag) is signalled at the CU level. Moreover,when the FRUC mode is applied (for example, when the FRUC flag is set totrue), information indicating the pattern matching method (first patternmatching or second pattern matching) is signalled at the CU level. Notethat the signaling of such information need not be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

Here, a mode for deriving a motion vector based on a model assuminguniform linear motion will be described. This mode is also referred toas a bi-directional optical flow (BIO) mode.

FIG. 8 is for illustrating a model assuming uniform linear motion. InFIG. 8, (v_(x), v_(y)) denotes a velocity vector, and τ₀ and τ₁ denotetemporal distances between the current picture (Cur Pic) and tworeference pictures (Ref₀, Ref₁). (MVx₀, MVy₀) denotes a motion vectorcorresponding to reference picture Ref₀, and (MVx₁, MVy₁) denotes amotion vector corresponding to reference picture Ref₁.

Here, under the assumption of uniform linear motion exhibited byvelocity vector (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x)τ₀, v_(y)τ₀) and (−v_(x)τ₁, −v_(y)τ₁),respectively, and the following optical flow equation is given.

MATH. 1

∂I ^((k)) /∂t+v _(x) ∂I ^((k)) /∂x+v _(y) ∂I ^((k)) /∂y=0.  (1)

Here, I^((k)) denotes a luma value from reference picture k (k=0, 1)after motion compensation. This optical flow equation shows that the sumof (i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference picture, and (iii) the product of the vertical velocityand the vertical component of the spatial gradient of a referencepicture is equal to zero. A motion vector of each block obtained from,for example, a merge list is corrected pixel by pixel based on acombination of the optical flow equation and Hermite interpolation.

Note that a motion vector may be derived on the decoder side using amethod other than deriving a motion vector based on a model assuminguniform linear motion. For example, a motion vector may be derived foreach sub-block based on motion vectors of neighboring blocks.

Here, a mode in which a motion vector is derived for each sub-blockbased on motion vectors of neighboring blocks will be described. Thismode is also referred to as affine motion compensation prediction mode.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks. In FIG. 9A, the currentblock includes 16 4×4 sub-blocks. Here, motion vector v₀ of the top leftcorner control point in the current block is derived based on motionvectors of neighboring sub-blocks, and motion vector v₁ of the top rightcorner control point in the current block is derived based on motionvectors of neighboring blocks. Then, using the two motion vectors v₀ andv₁, the motion vector (v_(x), v_(y)) of each sub-block in the currentblock is derived using Equation 2 below.

MATH.2 $\begin{matrix}\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0_{y}}} \right)}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0_{y}}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0_{y}}}}\end{matrix} \right. & (2)\end{matrix}$

Here, x and y are the horizontal and vertical positions of thesub-block, respectively, and w is a determined weighted coefficient. Thedetermined weighted coefficient may be predetermined.

Such an affine motion compensation prediction mode may include a numberof modes of different methods of deriving the motion vectors of the topleft and top right corner control points. Information indicating such anaffine motion compensation prediction mode (referred to as, for example,an affine flag) is signalled at the CU level. Note that the signaling ofinformation indicating the affine motion compensation prediction modeneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, CTU level, or sub-block level).

[Prediction Controller]

Prediction controller 128 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto subtractor 104 and adder 116.

Here, an example of deriving a motion vector via merge mode in a currentpicture will be given. FIG. 9B is for illustrating an outline of aprocess for deriving a motion vector via merge mode.

First, an MV predictor list in which candidate MV predictors areregistered is generated. Examples of candidate MV predictors include:spatially neighboring MV predictors, which are MVs of encoded blockspositioned in the spatial vicinity of the current block; a temporallyneighboring MV predictor, which is an MV of a block in an encodedreference picture that neighbors a block in the same location as thecurrent block; a combined MV predictor, which is an MV generated bycombining the MV values of the spatially neighboring MV predictor andthe temporally neighboring MV predictor; and a zero MV predictor, whichis an MV whose value is zero.

Next, the MV of the current block is determined by selecting one MVpredictor from among the plurality of MV predictors registered in the MVpredictor list.

Furthermore, in the variable-length encoder, a merge_idx, which is asignal indicating which MV predictor is selected, is written and encodedinto the stream.

Note that the MV predictors registered in the MV predictor listillustrated in FIG. 9B constitute one example. The number of MVpredictors registered in the MV predictor list may be different from thenumber illustrated in FIG. 9B, the MV predictors registered in the MVpredictor list may omit one or more of the types of MV predictors givenin the example in FIG. 9B, and the MV predictors registered in the MVpredictor list may include one or more types of MV predictors inaddition to and different from the types given in the example in FIG.9B.

Note that the final MV may be determined by performing DMVR processing(to be described later) by using the MV of the current block derived viamerge mode.

Here, an example of determining an MV by using DMVR processing will begiven.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

First, the most appropriate MVP set for the current block is consideredto be the candidate MV, reference pixels are obtained from a firstreference picture, which is a picture processed in the L0 direction inaccordance with the candidate MV, and a second reference picture, whichis a picture processed in the L1 direction in accordance with thecandidate MV, and a template is generated by calculating the average ofthe reference pixels.

Next, using the template, the surrounding regions of the candidate MVsof the first and second reference pictures are searched, and the MV withthe lowest cost is determined to be the final MV. Note that the costvalue is calculated using, for example, the difference between eachpixel value in the template and each pixel value in the regionssearched, as well as the MV value.

Note that the outlines of the processes described here are fundamentallythe same in both the encoder and the decoder.

Note that processing other than the processing exactly as describedabove may be used, so long as the processing is capable of deriving thefinal MV by searching the surroundings of the candidate MV.

Here, an example of a mode that generates a prediction image by usingLIC processing will be given.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

First, an MV is extracted for obtaining, from an encoded referencepicture, a reference image corresponding to the current block.

Next, information indicating how the luminance value changed between thereference picture and the current picture is extracted and a luminancecorrection parameter is calculated by using the luminance pixel valuesfor the encoded left neighboring reference region and the encoded upperneighboring reference region, and the luminance pixel value in the samelocation in the reference picture specified by the MV.

The prediction image for the current block is generated by performing aluminance correction process by using the luminance correction parameteron the reference image in the reference picture specified by the MV.

Note that the shape of the surrounding reference region illustrated inFIG. 9D is just one example; the surrounding reference region may have adifferent shape.

Moreover, although a prediction image is generated from a singlereference picture in this example, in cases in which a prediction imageis generated from a plurality of reference pictures as well, theprediction image is generated after performing a luminance correctionprocess, via the same method, on the reference images obtained from thereference pictures.

One example of a method for determining whether to implement LICprocessing is by using an lic_flag, which is a signal that indicateswhether to implement LIC processing. As one specific example, theencoder determines whether the current block belongs to a region ofluminance change. The encoder sets the lic_flag to a value of “1” whenthe block belongs to a region of luminance change and implements LICprocessing when encoding, and sets the lic_flag to a value of “0” whenthe block does not belong to a region of luminance change and encodeswithout implementing LIC processing. The decoder switches betweenimplementing LIC processing or not by decoding the lic_flag written inthe stream and performing the decoding in accordance with the flagvalue.

One example of a different method of determining whether to implementLIC processing is determining so in accordance with whether LICprocessing was determined to be implemented for a surrounding block. Inone specific example, when merge mode is used on the current block,whether LIC processing was applied in the encoding of the surroundingencoded block selected upon deriving the MV in the merge mode processingmay be determined, and whether to implement LIC processing or not can beswitched based on the result of the determination. Note that in thisexample, the same applies to the processing performed on the decoderside.

[Decoder Outline]

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output from encoder 100 will be described. FIG. 10 is a blockdiagram illustrating a functional configuration of decoder 200 accordingto Embodiment 1. Decoder 200 is a moving picture/picture decoder thatdecodes a moving picture/picture block by block.

As illustrated in FIG. 10, decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220. Alternatively, decoder 200 may be realized as one or more dedicatedelectronic circuits corresponding to entropy decoder 202, inversequantizer 204, inverse transformer 206, adder 208, loop filter 212,intra predictor 216, inter predictor 218, and prediction controller 220.

Hereinafter, each component included in decoder 200 will be described.

[Entropy Decoder]

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically, for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204.

[Inverse Quantizer]

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block), whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedcoefficients (i.e., transform coefficients) of the current block toinverse transformer 206.

[Inverse Transformer]

Inverse transformer 206 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when the AMT flag is set totrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type.

Moreover, for example, when information parsed from an encoded bitstreamindicates application of NSST, inverse transformer 206 applies asecondary inverse transform to the transform coefficients.

[Adder]

Adder 208 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 206, and prediction samples,which is an input from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

[Block Memory]

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 210 storesreconstructed blocks output from adder 208.

[Loop Filter]

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214and, for example, a display device.

When information indicating the enabling or disabling of ALF parsed froman encoded bitstream indicates enabled, one filter from among aplurality of filters is selected based on direction and activity oflocal gradients, and the selected filter is applied to the reconstructedblock.

[Frame Memory]

Frame memory 214 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 214 stores reconstructed blocks filtered byloop filter 212.

[Intra Predictor]

Intra predictor 216 generates a prediction signal (intra predictionsignal) by intra prediction with reference to a block or blocks in thecurrent picture and stored in block memory 210. More specifically, intrapredictor 216 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 220.

Note that when an intra prediction mode in which a chroma block is intrapredicted from a luma block is selected, intra predictor 216 may predictthe chroma component of the current block based on the luma component ofthe current block.

Moreover, when information indicating the application of PDPC is parsedfrom an encoded bitstream, intra predictor 216 correctspost-intra-prediction pixel values based on horizontal/verticalreference pixel gradients.

[Inter Predictor]

Inter predictor 218 predicts the current block with reference to areference picture stored in frame memory 214. Inter prediction isperformed per current block or per sub-block (for example, per 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or sub-block by motioncompensation by using motion information (for example, a motion vector)parsed from an encoded bitstream, and outputs the inter predictionsignal to prediction controller 220.

Note that when the information parsed from the encoded bitstreamindicates application of OBMC mode, inter predictor 218 generates theinter prediction signal using motion information for a neighboring blockin addition to motion information for the current block obtained frommotion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates application of FRUC mode, inter predictor 218 derives motioninformation by performing motion estimation in accordance with thepattern matching method (bilateral matching or template matching) parsedfrom the encoded bitstream. Inter predictor 218 then performs motioncompensation using the derived motion information.

Moreover, when BIO mode is to be applied, inter predictor 218 derives amotion vector based on a model assuming uniform linear motion. Moreover,when the information parsed from the encoded bitstream indicates thataffine motion compensation prediction mode is to be applied, interpredictor 218 derives a motion vector of each sub-block based on motionvectors of neighboring blocks.

[Prediction Controller]

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208.

[First Aspect of Encoding and Decoding]

FIG. 11 illustrates an encoding method and encoding processing performedby encoder 100 according to a first aspect. Note that a decoding methodand decoding processing performed by decoder 200 are essentially thesame as the encoding method and encoding processing performed by encoder100. In the following description, “encode” or “encoding” in theencoding method and encoding processing can be replaced with “decode” or“decoding” in the decoding method and decoding processing.

First, encoder 100 splits an image block into a plurality of partitions(S101).

The image block may be split into four partitions, two partitions, orthree partitions, or may be split obliquely, as illustrated in FIG. 12A,FIG. 12B, FIG. 12C, FIG. 12D, FIG. 12E, FIG. 12F, FIG. 12G, FIG. 12H,FIG. 12I, and FIG. 12J. The way in which the image block is split is notlimited to those illustrated, and the illustrated ways of partitioningmay be freely combined.

Moreover, the partitions may be such partitions as those illustrated inFIG. 13A, FIG. 13B, FIG. 13C, FIG. 13D, and FIG. 13E. Specifically, apartition may be a rectangular partition, a non-rectangular partition, atriangular partition, an L-shape partition, a pentagonal partition, ahexagonal partition, or a polygonal partition.

Next, encoder 100 creates a motion vector candidate list for a partitionincluded in a plurality of partitions (S102). The motion vectorcandidate list may include at least one motion vector among a pluralityof motion vectors for a plurality of spatially neighboring partitions, aplurality of motion vectors for a plurality of temporally neighboringpartitions, and a plurality of motion vectors for a plurality ofsub-partitions.

A spatially neighboring partition is a partition that spatiallyneighbors the partition. The spatially neighboring partition may be apartition located at the top, left, right, bottom, top-left, top-right,bottom-left, or bottom-right of the partition.

A temporally neighboring partition is a partition that temporallyneighbors the partition. The temporally neighboring partition may be aco-located partition which, in a reference picture of the partition,corresponds to the position of the partition. The reference picture is apicture different from the current picture including the partition, andmay be a picture immediately before or immediately after the currentpicture. For example, the spatial position of the co-located partitionis the same as the position of the partition in the current picture.Alternatively, the spatial position, in the reference picture, of thetemporally neighboring partition may be different from the spatialposition, in the current picture, of the partition.

The plurality of motion vectors for the plurality of sub-partitionsinclude motion vectors predicted from motion vectors for sub-partitionswhich spatially or temporally neighbor the plurality of sub-partitions,and are obtained through sub-CU based motion vector predictionprocessing. The sub-CU based motion vector prediction processing may beadvanced temporal motion vector prediction (ATMVP), or may bespatial-temporal motion vector prediction (STMVP).

FIG. 14 illustrates an example of ATMVP processing. First, encoder 100splits an image block into a plurality of M×N sub-blocks (S201).Essentially, M and N are smaller than the width and the height of theimage block, respectively. M may be equal to N, but need not be equal toN. For example, M and N correspond to the horizontal pixel count of theimage block and the vertical pixel count of the image block,respectively.

Specifically, M may be 4. M may be one eighth of the width of the imageblock, or may be one Kth of the width of the image block, where K is apositive integer. Likewise, N may be 4. N may be one eighth of theheight of the image block, or may be one Kth of the height of the imageblock, where K is a positive integer.

Encoder 100 determines a corresponding block for the image block (S202).As illustrated in FIG. 15, the corresponding block is pointed by amotion vector derived from a spatially neighboring block of the imageblock. As illustrated in FIG. 16, encoder 100 then derives a motionvector for each of M×N sub-blocks based on motion information of thecorresponding block (S203).

FIG. 17 illustrates an example of STMVP processing. First, encoder 100splits an image block into a plurality of M×N sub-blocks (S301).Essentially, M and N are smaller than the width and the height of theimage block, respectively. M may be equal to N, but need not be equal toN. For example, M and N correspond to the horizontal pixel count of theimage block and the vertical pixel count of the image block,respectively.

Specifically, M may be 4. M may be one eighth of the width of the imageblock, or may be one Kth of the width of the image block, where K is apositive integer. Likewise, N may be 4. N may be one eighth of theheight of the image block, or may be one Kth of the height of the imageblock, where K is a positive integer.

Encoder 100 obtains three motion vectors for each of M×N sub-blocks(S302). Two of the three motion vectors are obtained from a spatiallyneighboring block of the M×N sub-block, whereas one of the three motionvectors is obtained from a temporally neighboring block of the M×Nsub-block. Encoder 100 derives, for each of the M×N sub-blocks, a motionvector obtained by averaging these three motion vectors (S303).

For example, the motion vector candidate list for the partition is thesame as the motion vector candidate list created for the image block ina determined prediction mode such as a merge mode or an inter predictionmode. The determined prediction mode may be predetermined.

Encoder 100 determines whether the partition is a triangular partition(S103). When the partition is not a triangular partition (NO at S103),encoder 100 performs a first method (S104). When the partition is atriangular partition (YES at S103), encoder 100 performs a second method(S105).

In the first method, encoder 100 performs first inter predictionprocessing on the partition using a first motion vector included in themotion vector candidate list (S104). For example, the first interprediction processing includes motion compensation processing,decoder-side motion vector refinement (DMVR) processing, andbi-directional optical flow (BIO) processing.

When the DMVR processing is to be performed, encoder 100 obtains aprediction image for the partition using the motion vector for thepartition. Encoder 100 then obtains a new motion vector for thepartition by, for example, performing motion estimation using theprediction image for the partition. Encoder 100 then obtains, as a finalprediction image for the partition, a new prediction image for thepartition using the new motion vector for the partition.

When the DMVR processing is not to be performed, encoder 100 obtains afinal prediction image for the partition using a normal motion vectorfor the partition, without using a new motion vector for the partition.For example, the normal motion vector may be a motion vector selectedfrom the motion vector candidate list.

FIG. 18 illustrates an example of the DMVR processing. Encoder 100determines whether the image block has two motion vectors including afirst motion vector and a second motion vector (S401). For example, whenthe image block does not have two motion vectors including the firstmotion vector and the second motion vector, encoder 100 derives aprediction block using one motion vector, and encodes the image blockusing the prediction block derived.

On the other hand, when the image block has two motion vectors includingthe first motion vector and the second motion vector, encoder 100derives a first prediction block and a second prediction block using thefirst motion vector and the second motion vector.

For example, the first motion vector points to the first referencepicture, and the second motion vector points to the second referencepicture. In such a case, encoder 100 predicts a first prediction blockusing the first motion vector and the first reference picture, andpredicts a second prediction block using the second motion vector andthe second reference picture (S402).

Next, encoder 100 performs weighting processing on the first predictionblock and the second prediction block, so as to derive a template blockas the result of the weighting processing (S403). Here, the weightingprocessing is, for example, weighted averaging or weighted addition.

Next, encoder 100 derives a third motion vector by performing motionestimation processing using the template block and the first referencepicture. Similarly, encoder 100 derives a fourth motion vector byperforming motion estimation processing using the template block and thesecond reference picture (S404). Here, the motion estimation processingis processing of estimating a motion vector by estimating a similarblock using block matching, for example.

Next, encoder 100 predicts a third prediction block using the thirdmotion vector and the first reference picture. Similarly, encoder 100predicts a fourth prediction block using the fourth motion vector andthe second reference picture (S405).

Next, encoder 100 performs the weighting processing on the thirdprediction block and the fourth prediction block (S406).

The DMVR processing is performed in the above described manner. Then,for example, encoder 100 encodes the image block using the result of theweighting processing (S407).

The DMVR processing is not limited to the above-described processing; itis sufficient so long as it is processing of determining a final motionvector by performing motion estimation based on a determined motionvector and an encoded reference picture. For example, a final motionvector may be estimated by performing cost evaluation using a differencevalue between the first prediction block and the second predictionblock, without creating the template block.

As described earlier, when the partition is a triangular partition,encoder 100 performs the second method (S105). In the second method,encoder 100 performs second inter prediction processing on the partitionusing the second motion vector included in the motion vector candidatelist.

For example, the second motion vector is different from the motionvectors for the sub-partitions. That is to say, the second motion vectoris different from the motion vectors derived through the sub-CU basedmotion vector prediction processing. The second inter predictionprocessing includes motion compensation processing, and does not includethe DMVR processing. The second inter prediction processing may includemotion compensation processing and BIO processing, and need not includethe DMVR processing.

Lastly, encoder 100 encodes the image block using the result of theinter prediction processing performed on the partition (S106). Forexample, encoder 100 performs the inter prediction processing, andobtains a prediction image as the result of the inter predictionprocessing. Encoder 100 then encodes the image block using theprediction image.

Encoder 100 performs the above-described processing (S102 to S105) oneach of the plurality of partitions, and may encode the image blockusing a plurality of results of the inter prediction processingperformed on the plurality of partitions.

Encoder 100 may encode a flag which indicates whether the image block isto be split into a plurality of partitions including a triangularpartition. This flag is also referred to as a split parameter. Forexample, when the flag is 1, it indicates that the image block is to besplit into a plurality of partitions including a triangular partition,whereas when the flag is 0, it indicates that the image block is not tobe split into a plurality of partitions including a triangularpartition.

The above flag may be a triangle flag indicating whether the mode is atriangle mode in which the image block is split into a plurality ofpartitions including a triangular partition, a motion vector is derivedfor each partition, and motion compensation is performed for eachpartition.

For example, in the triangle mode, the image block is split into aplurality of triangular partitions. Then, a candidate motion vector listis generated for each triangular partition. Then, for each triangularpartition, motion compensation processing is performed using a motionvector predicted from the candidate motion vector list. Then, predictionprocessing for the image block is performed by combining a plurality ofprediction images of the plurality of triangular partitions. Then, theimage block is encoded based on the result of the prediction processing.

The above flag may be encoded by the same flag as a flag related to adifferent prediction mode. For example, when the flag is a first value,it may indicate that the image block is to be encoded in the merge mode,whereas when the flag is a second value different from the first value,it may indicate that the image block is to be encoded in the trianglemode. The flag may indicate a method for splitting the image block.

When the flag indicates that the image block is to be split into aplurality of partitions including a triangular partition, encoder 100encodes the image block after splitting the image block into a pluralityof partitions including a triangular partition.

On the other hand, when the flag indicates that the image block is notto be split into a plurality of partitions including a triangularpartition, encoder 100 encodes the image block without splitting theimage block into a plurality of partitions including a triangularpartition. In such a case, encoder 100 may encode the image blockwithout splitting the image block, or may encode the image block aftersplitting the image block into a plurality of rectangular partitions.

As illustrated in FIG. 19, encoder 100 may encode the above flag basedon a determination result. In this example, encoder 100 first obtains aparameter of the image block (S501). The parameter of the image blockmay be at least one of the width of the image block, the height of theimage block, or a ratio of the width to the height of the image block.This parameter is also referred to as a size parameter.

Next, encoder 100 determines whether the parameter is greater than orequal to a first threshold and less than or equal to a second threshold(S502). When the parameter is greater than or equal to the firstthreshold and less than or equal to the second threshold (YES at S502),encoder 100 encodes the image block with a flag (S503). The firstthreshold is less than or equal to the second threshold. Essentially,the first threshold and the second threshold are greater than or equalto 0.

When the parameter is not greater than or equal to the first thresholdand less than or equal to the second threshold (NO at S502), that is,when the parameter is less than the first threshold or greater than thesecond threshold, encoder 100 encodes the image block without a flag(S504). Alternatively, when the parameter is not greater than or equalto the first threshold and less than or equal to the second threshold,encoder 100 may encode the image block with a flag indicating that theimage block is not to be split into a plurality of partitions includinga triangular partition.

The first threshold may be the reciprocal of the second threshold. Thefirst threshold may be a positive integer or a positive fraction. Thesecond threshold may also be a positive integer or a positive fraction.

For example, the parameter is a ratio of the width to the height of theimage block. The first threshold is the reciprocal of the secondthreshold. When the ratio of the width to the height of the image blockis greater than or equal to the first threshold and less than or equalto the second threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The firstthreshold and the second threshold are both a positive integer. Whenboth the width and the height of the image block are greater than orequal to the first threshold and less than or equal to the secondthreshold, encoder 100 encodes the image block with a flag (S503).Otherwise, encoder 100 encodes the image block without a flag (S504).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The firstthreshold and the second threshold are both a positive integer. When atleast one of the width or the height of the image block is greater thanor equal to the first threshold and less than or equal to the secondthreshold, encoder 100 encodes the image block with a flag (S503).Otherwise, encoder 100 encodes the image block without a flag (S504).

For example, two parameters including a first parameter and a secondparameter, and four thresholds including a first threshold, a secondthreshold, a third threshold, and a fourth threshold are used. The firstparameter is the width of the image block, and the second parameter is aratio of the width to the height of the image block. Each of the fourthresholds is a positive integer. The first threshold is less than orequal to the second threshold. The third threshold is the reciprocal ofthe fourth threshold.

When the first parameter is greater than or equal to the first thresholdand less than or equal to the second threshold, and the second parameteris greater than or equal to the third threshold and less than or equalto the fourth threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, two parameters including a first parameter and a secondparameter, and four thresholds including a first threshold, a secondthreshold, a third threshold, and a fourth threshold are used. The firstparameter is the width of the image block, and the second parameter isthe height of the image block. Each of the four thresholds is a positiveinteger. The first threshold is less than or equal to the secondthreshold. The third threshold is less than or equal to the fourththreshold.

When the first parameter is greater than or equal to the first thresholdand less than or equal to the second threshold, and the second parameteris greater than or equal to the third threshold and less than or equalto the fourth threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, three parameters including a first parameter, a secondparameter, and a third parameter, and four thresholds including a firstthreshold, a second threshold, a third threshold, and a fourth thresholdare used. The first parameter is the width of the image block, thesecond parameter is the height of the image block, and the thirdparameter is a ratio of the width to the height of the image block. Eachof the four thresholds is a positive integer. The first threshold isless than or equal to the second threshold. The third threshold is thereciprocal of the fourth threshold.

When both the first parameter and the second parameter are greater thanor equal to the first threshold and less than or equal to the secondthreshold, and the third parameter is greater than or equal to the thirdthreshold and less than or equal to the fourth threshold, encoder 100encodes the image block with a flag (S503). Otherwise, encoder 100encodes the image block without a flag (S504).

As illustrated in FIG. 20, encoder 100 may encode the above flag basedon a determination result. In this example, encoder 100 first obtains aparameter of the image block (S601). The parameter of the image blockmay be at least one of the width of the image block, the height of theimage block, or a ratio of the width to the height of the image block.This parameter is also referred to as a size parameter.

Next, encoder 100 determines whether the parameter is greater than orequal to a threshold (S602). When the parameter is greater than or equalto the threshold (YES at S602), encoder 100 encodes the image block witha flag (S603). Essentially, the threshold is greater than or equal to 0.

When the parameter is not greater than or equal to the threshold (NO atS602), that is, when the parameter is less than the threshold, encoder100 encodes the image block without a flag (S604). Alternatively, whenthe parameter is not greater than or equal to the threshold, encoder 100may encode the image block with a flag indicating that the image blockis not to be split into a plurality of partitions including a triangularpartition.

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The thresholdis a positive integer. When both the width and the height of the imageblock are greater than or equal to the threshold, encoder 100 encodesthe image block with a flag (S603). Otherwise, encoder 100 encodes theimage block without a flag (S604).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The thresholdis a positive integer. When at least one of the width or the height ofthe image block is greater than or equal to the threshold, encoder 100encodes the image block with a flag (S603). Otherwise, encoder 100encodes the image block without a flag (S604).

For example, the parameter is the width of the image block. Thethreshold is a positive integer. When the width of the image block isgreater than or equal to the threshold, encoder 100 encodes the imageblock with a flag (S603). Otherwise, encoder 100 encodes the image blockwithout a flag (S604).

When encoding the image block without a flag, encoder 100 may encode theimage block without splitting the image block, or may encode the imageblock after splitting the image block into a plurality of rectangularpartitions.

In the present aspect, inter prediction processing for triangularpartitions is simplified. Accordingly, software and hardware complexityis reduced.

[Second Aspect of Encoding and Decoding]

FIG. 21 illustrates an encoding method and encoding processing performedby encoder 100 according to a second aspect. Note that a decoding methodand decoding processing performed by decoder 200 are essentially thesame as the encoding method and encoding processing performed by encoder100. In the following description, “encode” or “encoding” in theencoding method and encoding processing can be replaced with “decode” or“decoding” in the decoding method and decoding processing.

First, encoder 100 splits an image block into a plurality of partitions(S701).

The image block may be split into four partitions, two partitions, orthree partitions, or may be split obliquely, as illustrated in FIG. 12A,FIG. 12B, FIG. 12C, FIG. 12D, FIG. 12E, FIG. 12F, FIG. 12G, FIG. 12H,FIG. 12I, and FIG. 12J. The way in which the image block is split is notlimited to those illustrated, and the illustrated ways of partitioningmay be freely combined.

Moreover, the partitions may be such partitions as those illustrated inFIG. 13A, FIG. 13B, FIG. 13C, FIG. 13D, and FIG. 13E. Specifically, apartition may be a rectangular partition, a non-rectangular partition, atriangular partition, an L-shape partition, a pentagonal partition, ahexagonal partition, or a polygonal partition.

Next, encoder 100 creates a motion vector candidate list for a partitionincluded in a plurality of partitions (S702). The motion vectorcandidate list may include at least one motion vector among a pluralityof motion vectors for a plurality of spatially neighboring partitions, aplurality of motion vectors for a plurality of temporally neighboringpartitions, and a plurality of motion vectors for a plurality ofsub-partitions.

A spatially neighboring partition is a partition that spatiallyneighbors the partition. The spatially neighboring partition may be apartition located at the top, left, right, bottom, top-left, top-right,bottom-left, or bottom-right of the partition.

A temporally neighboring partition is a partition that temporallyneighbors the partition. The temporally neighboring partition may be aco-located partition which, in a reference picture of the partition, islocated in a position that corresponds to the position of the partition.The reference picture is a picture different from the current pictureincluding the partition, and may be a picture immediately before orimmediately after the current picture. For example, the spatial positionof the co-located partition is the same as the position of the partitionin the current picture.

The plurality of motion vectors for the plurality of sub-partitionsinclude motion vectors predicted from motion vectors for sub-partitionswhich spatially or temporally neighbor the plurality of sub-partitions,and are obtained through sub-CU based motion vector predictionprocessing. The sub-CU based motion vector prediction processing may beATMVP, or may be STMVP.

For example, the motion vector candidate list for the partition is thesame as the motion vector candidate list created for the image block ina determined prediction mode such as a merge mode or an inter predictionmode. The determined prediction mode may be predetermined.

Encoder 100 determines whether the partition is a triangular partition(S703). When the partition is not a triangular partition (NO at S703),encoder 100 performs a first method (S704 and S705). When the partitionis a triangular partition (YES at S703), encoder 100 performs a secondmethod (S706 and S707).

In the first method, encoder 100 selects a first motion vector for thepartition from the motion vector candidate list (S704). Encoder 100 thenperforms first inter prediction processing on the partition using thefirst motion vector (S705). The first inter prediction processingincludes motion compensation processing.

For example, the first inter prediction processing may include OBMCprocessing. Alternatively, the first inter prediction processing mayinclude DMVR processing, BIO processing, and OBMC processing.

In the second method, encoder 100 selects, for the partition, a secondmotion vector which is not based on a sub-partition, from the motionvector candidate list (S706). For example, the second motion vectorwhich is not based on a sub-partition is a motion vector that is notderived from the sub-CU based motion vector prediction processing.Encoder 100 then performs second inter prediction processing on thepartition using the second motion vector (S707). The second interprediction processing includes motion compensation processing.

For example, the second inter prediction processing is the same as thefirst inter prediction processing. Alternatively, the second interprediction processing may include BIO processing, and need not includethe DMVR processing.

Lastly, encoder 100 encodes the image block using the result of interprediction processing performed on the partition (S708). For example,encoder 100 performs the inter prediction processing, and obtains aprediction image as the result of the inter prediction processing.Encoder 100 then encodes the image block using the prediction image.

Encoder 100 performs the above-described processing (S702 to S707) oneach of the plurality of partitions, and may encode the image blockusing a plurality of results of the inter prediction processingperformed on the plurality of partitions.

Encoder 100 may encode a flag which indicates whether the image block isto be split into a plurality of partitions including a triangularpartition. This flag is also referred to as a split parameter. Forexample, when the flag is 1, it indicates that the image block is to besplit into a plurality of partitions including a triangular partition,whereas when the flag is 0, it indicates that the image block is not tobe split into a plurality of partitions including a triangularpartition.

When the flag indicates that the image block is to be split into aplurality of partitions including a triangular partition, encoder 100encodes the image block after splitting the image block into a pluralityof partitions including a triangular partition.

On the other hand, when the flag indicates that the image block is notto be split into a plurality of partitions including a triangularpartition, encoder 100 encodes the image block without splitting theimage block into a plurality of partitions including a triangularpartition. In this case, encoder 100 may encode the image block withoutsplitting the image block, or may encode the image block after splittingthe image block into a plurality of rectangular partitions.

As illustrated in FIG. 19, encoder 100 may encode the above flag basedon a determination result. In this example, encoder 100 first obtains aparameter of the image block (S501). The parameter of the image blockmay be at least one of the width of the image block, the height of theimage block, or a ratio of the width to the height of the image block.This parameter is also referred to as a size parameter.

Next, encoder 100 determines whether the parameter is greater than orequal to a first threshold and less than or equal to a second threshold(S502). When the parameter is greater than or equal to the firstthreshold and less than or equal to the second threshold (YES at S502),encoder 100 encodes the image block with a flag (S503). The firstthreshold is less than or equal to the second threshold. Essentially,the first threshold and the second threshold are greater than or equalto 0.

When the parameter is not greater than or equal to the first thresholdand less than or equal to the second threshold (NO at S502), that is,when the parameter is less than the first threshold or greater than thesecond threshold, encoder 100 encodes the image block without a flag(S504). Alternatively, when the parameter is not greater than or equalto the first threshold and less than or equal to the second threshold,encoder 100 may encode the image block with a flag indicating that theimage block is not to be split into a plurality of partitions includinga triangular partition.

The first threshold may be the reciprocal of the second threshold. Thefirst threshold may be a positive integer or a positive fraction. Thesecond threshold may also be a positive integer or a positive fraction.

For example, the parameter is a ratio of the width to the height of theimage block. The first threshold is the reciprocal of the secondthreshold. When the ratio of the width to the height of the image blockis greater than or equal to the first threshold and less than or equalto the second threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The firstthreshold and the second threshold are both a positive integer. Whenboth the width and the height of the image block are greater than orequal to the first threshold and less than or equal to the secondthreshold, encoder 100 encodes the image block with a flag (S503).Otherwise, encoder 100 encodes the image block without a flag (S504).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The firstthreshold and the second threshold are both a positive integer. When atleast one of the width or the height of the image block is greater thanor equal to the first threshold and less than or equal to the secondthreshold, encoder 100 encodes the image block with a flag (S503).Otherwise, encoder 100 encodes the image block without a flag (S504).

For example, two parameters including a first parameter and a secondparameter, and four thresholds including a first threshold, a secondthreshold, a third threshold, and a fourth threshold are used. The firstparameter is the width of the image block, and the second parameter is aratio of the width to the height of the image block. Each of the fourthresholds is a positive integer. The first threshold is less than orequal to the second threshold. The third threshold is the reciprocal ofthe fourth threshold.

When the first parameter is greater than or equal to the first thresholdand less than or equal to the second threshold, and the second parameteris greater than or equal to the third threshold and less than or equalto the fourth threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, two parameters including a first parameter and a secondparameter, and four thresholds including a first threshold, a secondthreshold, a third threshold, and a fourth threshold are used. The firstparameter is the width of the image block, and the second parameter isthe height of the image block. Each of the four thresholds is a positiveinteger. The first threshold is less than or equal to the secondthreshold. The third threshold is less than or equal to the fourththreshold.

When the first parameter is greater than or equal to the first thresholdand less than or equal to the second threshold, and the second parameteris greater than or equal to the third threshold and less than or equalto the fourth threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, three parameters including a first parameter, a secondparameter, and a third parameter, and four thresholds including a firstthreshold, a second threshold, a third threshold, and a fourth thresholdare used. The first parameter is the width of the image block, thesecond parameter is the height of the image block, and the thirdparameter is a ratio of the width to the height of the image block. Eachof the four thresholds is a positive integer. The first threshold isless than or equal to the second threshold. The third threshold is thereciprocal of the fourth threshold.

When both the first parameter and the second parameter are greater thanor equal to the first threshold and less than or equal to the secondthreshold, and the third parameter is greater than or equal to the thirdthreshold and less than or equal to the fourth threshold, encoder 100encodes the image block with a flag (S503). Otherwise, encoder 100encodes the image block without a flag (S504).

As illustrated in FIG. 20, encoder 100 may encode the above flag basedon a determination result. In this example, encoder 100 first obtains aparameter of the image block (S601). The parameter of the image blockmay be at least one of the width of the image block, the height of theimage block, or a ratio of the width to the height of the image block.This parameter is also referred to as a size parameter.

Next, encoder 100 determines whether the parameter is greater than orequal to a threshold (S602). When the parameter is greater than or equalto the threshold (YES at S602), encoder 100 encodes the image block witha flag (S603). Essentially, the threshold is greater than or equal to 0.

When the parameter is not greater than or equal to the threshold (NO atS602), that is, when the parameter is less than the threshold, encoder100 encodes the image block without a flag (S604). Alternatively, whenthe parameter is not greater than or equal to the threshold, encoder 100may encode the image block with a flag indicating that the image blockis not to be split into a plurality of partitions including a triangularpartition.

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The thresholdis a positive integer. When both the width and the height of the imageblock are greater than or equal to the threshold, encoder 100 encodesthe image block with a flag (S603). Otherwise, encoder 100 encodes theimage block without a flag (S604).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The thresholdis a positive integer. When at least one of the width or the height ofthe image block is greater than or equal to the threshold, encoder 100encodes the image block with a flag (S603). Otherwise, encoder 100encodes the image block without a flag (S604).

For example, the parameter is the width of the image block. Thethreshold is a positive integer. When the width of the image block isgreater than or equal to the threshold, encoder 100 encodes the imageblock with a flag (S603). Otherwise, encoder 100 encodes the image blockwithout a flag (S604).

When encoding the image block without a flag, encoder 100 may encode theimage block without splitting the image block, or may encode the imageblock after splitting the image block into a plurality of rectangularpartitions.

In the present aspect, motion vector prediction processing fortriangular partitions is simplified, thus reducing the operation amount.

Note that encoder 100 may generate the motion vector candidate listafter determining whether the partition is a triangular partition. Forexample, when the partition is not a triangular partition, encoder 100may generate the motion vector candidate list which includes asub-partition-based motion vector. When the partition is a triangularpartition, encoder 100 may generate the motion vector candidate listwhich does not include a sub-partition-based motion vector.

Accordingly, when the partition is not a triangular partition, encoder100 can select a first motion vector from the motion vector candidatelist which includes a sub-partition-based motion vector. When thepartition is a triangular partition, encoder 100 can select a secondmotion vector that is not based on a sub-partition, from the motionvector candidate list which does not include a sub-partition-basedmotion vector.

[Third Aspect of Encoding and Decoding]

FIG. 22 illustrates an encoding method and encoding processing performedby encoder 100 according to a third aspect. Note that a decoding methodand decoding processing performed by decoder 200 are essentially thesame as the encoding method and encoding processing performed by encoder100. In the following description, “encode” or “encoding” in theencoding method and encoding processing can be replaced with “decode” or“decoding” in the decoding method and decoding processing.

First, encoder 100 splits an image block into a plurality of partitions(S801).

The image block may be split into four partitions, two partitions, orthree partitions, or may be split obliquely, as illustrated in FIG. 12A,FIG. 12B, FIG. 12C, FIG. 12D, FIG. 12E, FIG. 12F, FIG. 12G, FIG. 12H,FIG. 12I, and FIG. 12J. The way in which the image block is split is notlimited to those illustrated, and the illustrated ways of partitioningmay be freely combined.

Moreover, the partitions may be such partitions as those illustrated inFIG. 13A, FIG. 13B, FIG. 13C, FIG. 13D, and FIG. 13E. Specifically, apartition may be a rectangular partition, a non-rectangular partition, atriangular partition, an L-shape partition, a pentagonal partition, ahexagonal partition, or a polygonal partition.

Next, encoder 100 creates a motion vector candidate list for a partitionincluded in a plurality of partitions (S802). The motion vectorcandidate list may include at least one motion vector among a pluralityof motion vectors for a plurality of spatially neighboring partitions, aplurality of motion vectors for a plurality of temporally neighboringpartitions, and a plurality of motion vectors for a plurality ofsub-partitions.

A spatially neighboring partition is a partition that spatiallyneighbors the partition. The spatially neighboring partition may be apartition located at the top, left, right, bottom, top-left, top-right,bottom-left, or bottom-right of the partition.

A temporally neighboring partition is a partition that temporallyneighbors the partition. The temporally neighboring partition may be aco-located partition which, in a reference picture of the partition, islocated in a position that corresponds to the position of the partition.The reference picture is a picture different from the current pictureincluding the partition, and may be a picture immediately before orimmediately after the current picture. For example, the spatial positionof the co-located partition is the same as the position of the partitionin the current picture.

The plurality of motion vectors for the plurality of sub-partitionsinclude motion vectors predicted from motion vectors for sub-partitionswhich spatially or temporally neighbor the plurality of sub-partitions,and are obtained through sub-CU based motion vector predictionprocessing. The sub-CU based motion vector prediction processing may beATMVP, or may be STMVP.

For example, the motion vector candidate list for the partition is thesame as the motion vector candidate list created for the image block ina determined prediction mode such as a merge mode or an inter predictionmode. The determined prediction mode may be predetermined.

Encoder 100 determines whether the partition is a triangular partition(S803). When the partition is not a triangular partition (NO at S803),encoder 100 performs a first method (S804). When the partition is atriangular partition (YES at S803), encoder 100 performs a second method(S805).

In the first method, encoder 100 performs first inter predictionprocessing on the partition using a motion vector included in the motionvector candidate list (S804). For example, the first inter predictionprocessing includes motion compensation processing and DMVR processing.The first inter prediction processing may include BIO processing, butneed not include BIO processing.

For example, a prediction image obtained for the partition using thefirst method is the same as a portion corresponding to the partition, ofa prediction image obtained for the image block without splitting theimage block in a determined prediction mode such as a merge mode or aninter prediction mode. The determined prediction mode may bepredetermined.

In the second method, encoder 100 performs second inter predictionprocessing on the partition using a motion vector included in the motionvector candidate list (S805). For example, the second inter predictionprocessing includes motion compensation processing, and does not includethe DMVR processing. The second inter prediction processing may includeBIO processing, but need not include BIO processing.

Lastly, encoder 100 encodes the image block using the result of interprediction processing performed on the partition (S806). For example,encoder 100 performs the inter prediction processing, and obtains aprediction image as the result of the inter prediction processing.Encoder 100 then encodes the image block using the prediction image.

Encoder 100 performs the above-described processing (S802 to S805) oneach of the plurality of partitions, and may encode the image blockusing a plurality of results of the inter prediction processingperformed on the plurality of partitions.

Encoder 100 may encode a flag which indicates whether the image block isto be split into a plurality of partitions including a triangularpartition. This flag is also referred to as a split parameter. Forexample, when the flag is 1, it indicates that the image block is to besplit into a plurality of partitions including a triangular partition,whereas when the flag is 0, it indicates that the image block is not tobe split into a plurality of partitions including a triangularpartition.

When the flag indicates that the image block is to be split into aplurality of partitions including a triangular partition, encoder 100encodes the image block after splitting the image block into a pluralityof partitions including a triangular partition.

On the other hand, when the flag indicates that the image block is notto be split into a plurality of partitions including a triangularpartition, encoder 100 encodes the image block without splitting theimage block into a plurality of partitions including a triangularpartition. In this case, encoder 100 may encode the image block withoutsplitting the image block, or may encode the image block after splittingthe image block into a plurality of rectangular partitions.

As illustrated in FIG. 19, encoder 100 may encode the above flag basedon a determination result. In this example, encoder 100 first obtains aparameter of the image block (S501). The parameter of the image blockmay be at least one of the width of the image block, the height of theimage block, or a ratio of the width to the height of the image block.This parameter is also referred to as a size parameter.

Next, encoder 100 determines whether the parameter is greater than orequal to a first threshold and less than or equal to a second threshold(S502). When the parameter is greater than or equal to the firstthreshold and less than or equal to the second threshold (YES at S502),encoder 100 encodes the image block with a flag (S503). The firstthreshold is less than or equal to the second threshold. Essentially,the first threshold and the second threshold are greater than or equalto 0.

When the parameter is not greater than or equal to the first thresholdand less than or equal to the second threshold (NO at S502), that is,when the parameter is less than the first threshold or greater than thesecond threshold, encoder 100 encodes the image block without a flag(S504). Alternatively, when the parameter is not greater than or equalto the first threshold and less than or equal to the second threshold,encoder 100 may encode the image block with a flag indicating that theimage block is not to be split into a plurality of partitions includinga triangular partition.

The first threshold may be the reciprocal of the second threshold. Thefirst threshold may be a positive integer or a positive fraction. Thesecond threshold may also be a positive integer or a positive fraction.

For example, the parameter is a ratio of the width to the height of theimage block. The first threshold is the reciprocal of the secondthreshold. When the ratio of the width to the height of the image blockis greater than or equal to the first threshold and less than or equalto the second threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The firstthreshold and the second threshold are both a positive integer. Whenboth the width and the height of the image block are greater than orequal to the first threshold and less than or equal to the secondthreshold, encoder 100 encodes the image block with a flag (S503).Otherwise, encoder 100 encodes the image block without a flag (S504).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The firstthreshold and the second threshold are both a positive integer. When atleast one of the width or the height of the image block is greater thanor equal to the first threshold and less than or equal to the secondthreshold, encoder 100 encodes the image block with a flag (S503).Otherwise, encoder 100 encodes the image block without a flag (S504).

For example, two parameters including a first parameter and a secondparameter, and four thresholds including a first threshold, a secondthreshold, a third threshold, and a fourth threshold are used. The firstparameter is the width of the image block, and the second parameter is aratio of the width to the height of the image block. Each of the fourthresholds is a positive integer. The first threshold is less than orequal to the second threshold. The third threshold is the reciprocal ofthe fourth threshold.

When the first parameter is greater than or equal to the first thresholdand less than or equal to the second threshold, and the second parameteris greater than or equal to the third threshold and less than or equalto the fourth threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, two parameters including a first parameter and a secondparameter, and four thresholds including a first threshold, a secondthreshold, a third threshold, and a fourth threshold are used. The firstparameter is the width of the image block, and the second parameter isthe height of the image block. Each of the four thresholds is a positiveinteger. The first threshold is less than or equal to the secondthreshold. The third threshold is less than or equal to the fourththreshold.

When the first parameter is greater than or equal to the first thresholdand less than or equal to the second threshold, and the second parameteris greater than or equal to the third threshold and less than or equalto the fourth threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, three parameters including a first parameter, a secondparameter, and a third parameter, and four thresholds including a firstthreshold, a second threshold, a third threshold, and a fourth thresholdare used. The first parameter is the width of the image block, thesecond parameter is the height of the image block, and the thirdparameter is a ratio of the width to the height of the image block. Eachof the four thresholds is a positive integer. The first threshold isless than or equal to the second threshold. The third threshold is thereciprocal of the fourth threshold.

When both the first parameter and the second parameter are greater thanor equal to the first threshold and less than or equal to the secondthreshold, and the third parameter is greater than or equal to the thirdthreshold and less than or equal to the fourth threshold, encoder 100encodes the image block with a flag (S503). Otherwise, encoder 100encodes the image block without a flag (S504).

As illustrated in FIG. 20, encoder 100 may encode the above flag basedon a determination result. In this example, encoder 100 first obtains aparameter of the image block (S601). The parameter of the image blockmay be at least one of the width of the image block, the height of theimage block, or a ratio of the width to the height of the image block.This parameter is also referred to as a size parameter.

Next, encoder 100 determines whether the parameter is greater than orequal to a threshold (S602). When the parameter is greater than or equalto the threshold (YES at S602), encoder 100 encodes the image block witha flag (S603). Essentially, the threshold is greater than or equal to 0.

When the parameter is not greater than or equal to the threshold (NO atS602), that is, when the parameter is less than the threshold, encoder100 encodes the image block without a flag (S604). Alternatively, whenthe parameter is not greater than or equal to the threshold, encoder 100may encode the image block with a flag indicating that the image blockis not to be split into a plurality of partitions including a triangularpartition.

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The thresholdis a positive integer. When both the width and the height of the imageblock are greater than or equal to the threshold, encoder 100 encodesthe image block with a flag (S603). Otherwise, encoder 100 encodes theimage block without a flag (S604).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The thresholdis a positive integer. When at least one of the width or the height ofthe image block is greater than or equal to the threshold, encoder 100encodes the image block with a flag (S603). Otherwise, encoder 100encodes the image block without a flag (S604).

For example, the parameter is the width of the image block. Thethreshold is a positive integer. When the width of the image block isgreater than or equal to the threshold, encoder 100 encodes the imageblock with a flag (S603). Otherwise, encoder 100 encodes the image blockwithout a flag (S604).

When encoding the image block without a flag, encoder 100 may encode theimage block without splitting the image block, or may encode the imageblock after splitting the image block into a plurality of rectangularpartitions.

In the present aspect, decoder-side motion vector refinement processingfor triangular partitions is eliminated, and the inter predictionprocessing for triangular partitions is simplified. Accordingly,software and hardware complexity is reduced.

[Fourth Aspect of Encoding and Decoding]

FIG. 23 illustrates an encoding method and encoding processing performedby encoder 100 according to a fourth aspect. Note that a decoding methodand decoding processing performed by decoder 200 are essentially thesame as the encoding method and encoding processing performed by encoder100. In the following description, “encode” or “encoding” in theencoding method and encoding processing can be replaced with “decode” or“decoding” in the decoding method and decoding processing.

First, encoder 100 splits an image block into a plurality of partitions(S901).

The image block may be split into four partitions, two partitions, orthree partitions, or may be split obliquely, as illustrated in FIG. 12A,FIG. 12B, FIG. 12C, FIG. 12D, FIG. 12E, FIG. 12F, FIG. 12G, FIG. 12H,FIG. 12I, and FIG. 12J. The way in which the image block is split is notlimited to those illustrated, and the illustrated ways of partitioningmay be freely combined.

Moreover, the partitions may be such partitions as those illustrated inFIG. 13A, FIG. 13B, FIG. 13C, FIG. 13D, and FIG. 13E. Specifically, apartition may be a rectangular partition, a non-rectangular partition, atriangular partition, an L-shape partition, a pentagonal partition, ahexagonal partition, or a polygonal partition.

Next, encoder 100 creates a motion vector candidate list for a partitionincluded in a plurality of partitions (S902). The motion vectorcandidate list may include at least one motion vector among a pluralityof motion vectors for a plurality of spatially neighboring partitions, aplurality of motion vectors for a plurality of temporally neighboringpartitions, and a plurality of motion vectors for a plurality ofsub-partitions.

A spatially neighboring partition is a partition that spatiallyneighbors the partition. The spatially neighboring partition may be apartition located at the top, left, right, bottom, top-left, top-right,bottom-left, or bottom-right of the partition.

A temporally neighboring partition is a partition that temporallyneighbors the partition. The temporally neighboring partition may be aco-located partition which, in a reference picture of the partition, islocated in a position that corresponds to the position of the partition.The reference picture is a picture different from the current pictureincluding the partition, and may be a picture immediately before orimmediately after the current picture. For example, the spatial positionof the co-located partition is the same as the position of the partitionin the current picture.

The plurality of motion vectors for the plurality of sub-partitionsinclude motion vectors predicted from motion vectors for sub-partitionswhich spatially or temporally neighbor the plurality of sub-partitions,and are obtained through sub-CU based motion vector predictionprocessing. The sub-CU based motion vector prediction processing may beATMVP, or may be STMVP.

For example, the motion vector candidate list for the partition is thesame as the motion vector candidate list created for the image block ina determined prediction mode such as a merge mode or an inter predictionmode. The determined prediction mode may be predetermined.

Encoder 100 determines whether the partition is a triangular partition(S903). When the partition is not a triangular partition (NO at S903),encoder 100 performs a first method (S904). When the partition is atriangular partition (YES at S903), encoder 100 performs a second method(S905).

In the first method, encoder 100 performs first inter predictionprocessing on the partition using a motion vector included in the motionvector candidate list (S904). For example, the first inter predictionprocessing includes motion compensation processing and BIO processing.The first inter prediction processing may include DMVR processing, butneed not include DMVR processing.

For example, a prediction image obtained for the partition using thefirst method is the same as a portion corresponding to the partition, ofa prediction image obtained for the image block without splitting theimage block in a determined prediction mode such as a merge mode or aninter prediction mode. The determined prediction mode may bepredetermined.

In the second method, encoder 100 performs second inter predictionprocessing on the partition using a motion vector included in the motionvector candidate list (S905). For example, the second inter predictionprocessing includes motion compensation processing, and does not includeBIO processing. The second inter prediction processing may include DMVRprocessing, but need not include DMVR processing.

Lastly, encoder 100 encodes the image block using the result of interprediction processing performed on the partition (S906). For example,encoder 100 performs the inter prediction processing, and obtains aprediction image as the result of the inter prediction processing.Encoder 100 then encodes the image block using the prediction image.

Encoder 100 performs the above-described processing (S902 to S905) oneach of the plurality of partitions, and may encode the image blockusing a plurality of results of the inter prediction processingperformed on the plurality of partitions.

Encoder 100 may encode a flag which indicates whether the image block isto be split into a plurality of partitions including a triangularpartition. This flag is also referred to as a split parameter. Forexample, when the flag is 1, it indicates that the image block is to besplit into a plurality of partitions including a triangular partition,whereas when the flag is 0, it indicates that the image block is not tobe split into a plurality of partitions including a triangularpartition.

When the flag indicates that the image block is to be split into aplurality of partitions including a triangular partition, encoder 100encodes the image block after splitting the image block into a pluralityof partitions including a triangular partition.

On the other hand, when the flag indicates that the image block is notto be split into a plurality of partitions including a triangularpartition, encoder 100 encodes the image block without splitting theimage block into a plurality of partitions including a triangularpartition. In this case, encoder 100 may encode the image block withoutsplitting the image block, or may encode the image block after splittingthe image block into a plurality of rectangular partitions.

As illustrated in FIG. 19, encoder 100 may encode the above flag basedon a determination result. In this example, encoder 100 first obtains aparameter of the image block (S501). The parameter of the image blockmay be at least one of the width of the image block, the height of theimage block, or a ratio of the width to the height of the image block.This parameter is also referred to as a size parameter.

Next, encoder 100 determines whether the parameter is greater than orequal to a first threshold and less than or equal to a second threshold(S502). When the parameter is greater than or equal to the firstthreshold and less than or equal to the second threshold (YES at S502),encoder 100 encodes the image block with a flag (S503). The firstthreshold is less than or equal to the second threshold. Essentially,the first threshold and the second threshold are greater than or equalto 0.

When the parameter is not greater than or equal to the first thresholdand less than or equal to the second threshold (NO at S502), that is,when the parameter is less than the first threshold or greater than thesecond threshold, encoder 100 encodes the image block without a flag(S504). Alternatively, when the parameter is not greater than or equalto the first threshold and less than or equal to the second threshold,encoder 100 may encode the image block with a flag indicating that theimage block is not to be split into a plurality of partitions includinga triangular partition.

The first threshold may be the reciprocal of the second threshold. Thefirst threshold may be a positive integer or a positive fraction. Thesecond threshold may also be a positive integer or a positive fraction.

For example, the parameter is a ratio of the width to the height of theimage block. The first threshold is the reciprocal of the secondthreshold. When the ratio of the width to the height of the image blockis greater than or equal to the first threshold and less than or equalto the second threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The firstthreshold and the second threshold are both a positive integer. Whenboth the width and the height of the image block are greater than orequal to the first threshold and less than or equal to the secondthreshold, encoder 100 encodes the image block with a flag (S503).Otherwise, encoder 100 encodes the image block without a flag (S504).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The firstthreshold and the second threshold are both a positive integer. When atleast one of the width or the height of the image block is greater thanor equal to the first threshold and less than or equal to the secondthreshold, encoder 100 encodes the image block with a flag (S503).Otherwise, encoder 100 encodes the image block without a flag (S504).

For example, two parameters including a first parameter and a secondparameter, and four thresholds including a first threshold, a secondthreshold, a third threshold, and a fourth threshold are used. The firstparameter is the width of the image block, and the second parameter is aratio of the width to the height of the image block. Each of the fourthresholds is a positive integer. The first threshold is less than orequal to the second threshold. The third threshold is the reciprocal ofthe fourth threshold.

When the first parameter is greater than or equal to the first thresholdand less than or equal to the second threshold, and the second parameteris greater than or equal to the third threshold and less than or equalto the fourth threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, two parameters including a first parameter and a secondparameter, and four thresholds including a first threshold, a secondthreshold, a third threshold, and a fourth threshold are used. The firstparameter is the width of the image block, and the second parameter isthe height of the image block. Each of the four thresholds is a positiveinteger. The first threshold is less than or equal to the secondthreshold. The third threshold is less than or equal to the fourththreshold.

When the first parameter is greater than or equal to the first thresholdand less than or equal to the second threshold, and the second parameteris greater than or equal to the third threshold and less than or equalto the fourth threshold, encoder 100 encodes the image block with a flag(S503). Otherwise, encoder 100 encodes the image block without a flag(S504).

For example, three parameters including a first parameter, a secondparameter, and a third parameter, and four thresholds including a firstthreshold, a second threshold, a third threshold, and a fourth thresholdare used. The first parameter is the width of the image block, thesecond parameter is the height of the image block, and the thirdparameter is a ratio of the width to the height of the image block. Eachof the four thresholds is a positive integer. The first threshold isless than or equal to the second threshold. The third threshold is thereciprocal of the fourth threshold.

When both the first parameter and the second parameter are greater thanor equal to the first threshold and less than or equal to the secondthreshold, and the third parameter is greater than or equal to the thirdthreshold and less than or equal to the fourth threshold, encoder 100encodes the image block with a flag (S503). Otherwise, encoder 100encodes the image block without a flag (S504).

As illustrated in FIG. 20, encoder 100 may encode the above flag basedon a determination result. In this example, encoder 100 first obtains aparameter of the image block (S601). The parameter of the image blockmay be at least one of the width of the image block, the height of theimage block, or a ratio of the width to the height of the image block.This parameter is also referred to as a size parameter.

Next, encoder 100 determines whether the parameter is greater than orequal to a threshold (S602). When the parameter is greater than or equalto the threshold (YES at S602), encoder 100 encodes the image block witha flag (S603). Essentially, the threshold is greater than or equal to 0.

When the parameter is not greater than or equal to the threshold (NO atS602), that is, when the parameter is less than the threshold, encoder100 encodes the image block without a flag (S604). Alternatively, whenthe parameter is not greater than or equal to the threshold, encoder 100may encode the image block with a flag indicating that the image blockis not to be split into a plurality of partitions including a triangularpartition.

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The thresholdis a positive integer. When both the width and the height of the imageblock are greater than or equal to the threshold, encoder 100 encodesthe image block with a flag (S603). Otherwise, encoder 100 encodes theimage block without a flag (S604).

For example, two parameters including a first parameter and a secondparameter are used. The first parameter is the width of the image block,and the second parameter is the height of the image block. The thresholdis a positive integer. When at least one of the width or the height ofthe image block is greater than or equal to the threshold, encoder 100encodes the image block with a flag (S603). Otherwise, encoder 100encodes the image block without a flag (S604).

For example, the parameter is the width of the image block. Thethreshold is a positive integer. When the width of the image block isgreater than or equal to the threshold, encoder 100 encodes the imageblock with a flag (S603). Otherwise, encoder 100 encodes the image blockwithout a flag (S604).

When encoding the image block without a flag, encoder 100 may encode theimage block without splitting the image block, or may encode the imageblock after splitting the image block into a plurality of rectangularpartitions.

In the present aspect, bi-directional optical flow processing fortriangular partitions is eliminated, and the inter prediction processingfor triangular partitions is simplified. Accordingly, software andhardware complexity is reduced.

[Modified Aspect of Encoding and Decoding]

The triangular partition mentioned in the above description may bereplaced with a non-rectangular partition. The processing may beswitched depending on whether the partition is a non-rectangularpartition. In doing so, the partition may be determined to be anon-rectangular partition when the partition is a triangular partition.

A non-rectangular partition may be an L-shape partition, a pentagonalpartition, a hexagonal partition, or a polygonal partition asillustrated in FIG. 13A, FIG. 13B, FIG. 13C, FIG. 13D, and FIG. 13E. Theimage block may be split into a plurality of partitions including atleast one of a non-rectangular partition or a rectangular partition.

The non-rectangular partition in the above description means a partitionother than a rectangular partition. The non-rectangular partition is notlimited to any of the plurality of partitions illustrated in FIG. 13A,FIG. 13B, FIG. 13C, FIG. 13D, and FIG. 13E. These partitions may befreely combined.

The partition in the above description may be replaced with a predictionunit. The partition may also be replaced with a sub-prediction unit. Theimage block in the above description may be replaced with a coding unit.The image block may also be replaced with a coding tree unit.

The ratio related to the size of the image block may be a ratio of thewidth to the height, or may be a ratio of the height to the width. Oneor more thresholds that are compared with a parameter related to thesize of the image block may indicate a restricted range of the ratio ofthe width of the image block to the height of the image block. Here, therestricted range is a range for splitting the image block into aplurality of partitions including a non-rectangular partition.

When BIO processing is to be performed, encoder 100 obtains a gradientimage for a prediction image, and obtains a final prediction image usingthe prediction image and the gradient image. Encoder 100 may obtain thegradient image by applying a filter to the prediction image to extract adifference value between pixels. When BIO processing is not to beperformed, encoder 100 obtains, as a final prediction image, aprediction image obtained without using a gradient image.

The first aspect, second aspect, third aspect, and fourth aspect in theabove description can be freely combined.

[Implementation Example]

FIG. 24 is a block diagram illustrating an implementation example ofencoder 100. Encoder 100 includes circuitry 160 and memory 162. Forexample, the plurality of constituent elements of encoder 100illustrated in FIG. 1 are implemented by circuitry 160 and memory 162illustrated in FIG. 24.

Circuitry 160 is electronic circuitry accessible to memory 162, andperforms information processing. For example, circuitry 160 is exclusiveor general electronic circuitry which encodes a video using memory 162.Circuitry 160 may be a processor such as a CPU. Circuitry 160 may be anaggregate of a plurality of electronic circuits.

Moreover, for example, circuitry 160 may perform the functions of two ormore constituent elements among the plurality of constituent elements ofencoder 100 illustrated in FIG. 1, except the constituent elements thatstore information. In other words, circuitry 160 may perform theabove-described operations as the operations of the two or moreconstituent elements.

Memory 162 is an exclusive or general memory for storing informationused by circuitry 160 to encode a video. Memory 162 may be an electroniccircuit, may be connected to circuitry 160, or may be included incircuitry 160.

Memory 162 may be an aggregate of a plurality of electronic circuits, ormay be configured in the form of a plurality of sub-memories. Memory 162may be a magnetic disc, an optical disc, or the like, or may beexpressed as storage, a recording medium, or the like. Memory 162 may bea non-volatile memory or a volatile memory.

For example, memory 162 may perform the functions of, among theplurality of constituent elements of encoder 100 illustrated in FIG. 1,the constituent elements that store information. Specifically, memory162 may perform the functions of block memory 118 and frame memory 122illustrated in FIG. 1.

Moreover, memory 162 may store a video to be encoded, or may store abitstream corresponding to an encoded video. Memory 162 may store aprogram for causing circuitry 160 to encode a video.

Note that not all of the plurality of constituent elements illustratedin FIG. 1 need to be implemented by encoder 100, and not all of theprocesses described above need to be performed by encoder 100. Some ofthe constituent elements illustrated in FIG. 1 may be included inanother device, and some of the processes described above may beperformed by another device. An image block can be efficiently processedby encoder 100 implementing some of the constituent elements illustratedin FIG. 1 and performing some of the processes described above.

FIG. 25 is a flow chart illustrating a first operation example ofencoder 100 illustrated in FIG. 24. For example, circuitry 160 includedin encoder 100 performs the operation illustrated in FIG. 25, usingmemory 162. Specifically, circuitry 160 encodes an image block (S1111).

For example, when encoding the image block, circuitry 160 obtains one ormore size parameters related to the size of the image block. Circuitry160 then determines whether the one or more size parameters and one ormore thresholds satisfy a determined relationship. The determinedrelationship may be predetermined.

Circuitry 160 then encodes a split parameter when the one or more sizeparameters and the one or more thresholds are determined to satisfy thedetermined relationship. Here, the split parameter indicates whether theimage block is to be split into a plurality of partitions including anon-rectangular partition. Circuitry 160 then encodes the image blockafter splitting the image block into the plurality of partitions whenthe split parameter indicates that the image block is to be split intothe plurality of partitions.

With this, encoder 100 can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters related to the size ofthe image block and the one or more thresholds satisfy the determinedrelationship. Accordingly, encoder 100 can efficiently process the imageblock.

For example, circuitry 160 encodes the image block without encoding thesplit parameter when the one or more size parameters and the one or morethresholds are determined not to satisfy the determined relationship.With this, the encoding amount can be reduced. Moreover, encoder 100 canreduce the amount of processing for encoding the split parameter.

For example, circuitry 160 encodes the image block without splitting theimage block or encodes the image block after splitting the image blockinto a plurality of rectangular partitions, when the one or more sizeparameters and the one or more thresholds are determined not to satisfythe determined relationship. With this, encoder 100 can reduce splittingof the image block into a plurality of partitions including anon-rectangular partition.

For example, circuitry 160 encodes the image block without splitting theimage block or encodes the image block after splitting the image blockinto a plurality of rectangular partitions, when the split parameterindicates that the image block is not to be split into the plurality ofpartitions. With this, encoder 100 can reduce splitting of the imageblock into a plurality of partitions including a non-rectangularpartition.

For example, the one or more thresholds comprise one threshold. Thedetermined relationship is that each of the one or more size parametersis greater than or equal to the one threshold, or that at least one ofthe one or more size parameters is greater than or equal to the onethreshold. With this, the encoder can switch whether or not to split theimage block into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters are greater than orequal to the one threshold.

For example, the one or more thresholds comprise a first threshold and asecond threshold, and the first threshold is less than or equal to thesecond threshold. The determined relationship is that each of the one ormore size parameters is greater than or equal to the first threshold andless than or equal to the second threshold, or that at least one of theone or more size parameters is greater than or equal to the firstthreshold and less than or equal to the second threshold. With this,encoder 100 can switch whether or not to split the image block into aplurality of partitions including a non-rectangular partition, when theone or more size parameters are greater than or equal to the firstthreshold and less than or equal to the second threshold.

For example, the non-rectangular partition is a triangular partition.With this, encoder 100 can switch whether or not to split the imageblock into a plurality of partitions including a triangular partition,when the one or more size parameters related to the size of the imageblock and the one or more thresholds satisfy the determinedrelationship.

For example, the one or more size parameters include at least one of aratio of the width of the image block to the height of the image block,a ratio of the height of the image block to the width of the imageblock, the width of the image block, or the height of the image block.With this, encoder 100 can use, as a size parameter, at least one of theratio of the width to the height of the image block, the ratio of theheight to the width of the image block, the width of the image block, orthe height of the image block.

For example, each of the one or more thresholds is greater than or equalto zero. With this, encoder 100 can switch whether or not to split theimage block into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters and the one or morethresholds, each of which is greater than or equal to zero, satisfy thedetermined relationship.

For example, the one or more thresholds indicate a restricted range of aratio of the width of the image block to the height of the image block.Here, the restricted range is a range for splitting the image block intothe plurality of partitions. With this, encoder 100 can switch whetheror not to split the image block into a plurality of partitions includinga non-rectangular partition, when the one or more size parameters andthe one or more thresholds, which indicate a restricted range of theratio of the width to the height, satisfy the determined relationship.

FIG. 26 is a flow chart illustrating a second operation example ofencoder 100 illustrated in FIG. 24. For example, circuitry 160 includedin encoder 100 performs the operations illustrated in FIG. 26, usingmemory 162. Specifically, circuitry 160 splits an image block into aplurality of partitions (S1121). Circuitry 160 then obtains a predictionimage for a partition included in the plurality of partitions (S1122).Circuitry 160 then encodes the image block using the prediction image(S1123).

For example, when obtaining the prediction image, circuitry 160determines whether the partition is a non-rectangular partition.

Here, when the partition is determined not to be a non-rectangularpartition, circuitry 160 obtains a first prediction image for thepartition using a first motion vector for the partition. Then, circuitry160 obtains a second motion vector for the partition using the firstprediction image, and obtains a second prediction image for thepartition as the prediction image using the second motion vector.

On the other hand, when the partition is determined to be anon-rectangular partition, circuitry 160 obtains the first predictionimage as the prediction image using the first motion vector, withoutusing the second motion vector.

With this, encoder 100 can reduce the two-step operation fornon-rectangular partitions, and suppress an increase in the processingamount. Accordingly, encoder 100 can efficiently process the imageblock.

For example, circuitry 160 determines that the partition is anon-rectangular partition when the partition is a triangular partition.With this, encoder 100 can suppress an increase in the processing amountfor triangular partitions.

For example, the prediction image obtained when the partition isdetermined not to be a non-rectangular partition is the same as aportion corresponding to the partition, of a prediction image obtainedfor the image block in a determined prediction mode. Here, theprediction image obtained for the image block in the determinedprediction mode is a prediction image obtained for the image blockwithout splitting the image block into the plurality of partitions. Thedetermined prediction mode may be predetermined.

With this, encoder 100 can obtain a prediction image for a rectangularpartition in the same manner as in the case of obtaining a predictionimage for the image block without splitting the image block into aplurality of partitions. Accordingly, encoder 100 can simplify theprocessing.

For example, circuitry 160 obtains the second motion vector byperforming motion estimation using the first prediction image. Withthis, encoder 100 can obtain an appropriate second motion vector usingthe first prediction image, and obtain an appropriate second predictionimage using the appropriate second motion vector.

For example, when obtaining the prediction image, circuitry 160determines whether the partition is a non-rectangular partition.

Here, when the partition is determined not to be a non-rectangularpartition, circuitry 160 obtains (i) a first prediction image for thepartition, (ii) a gradient image for the first prediction image, and(iii) a second prediction image as the prediction image using the firstprediction image and the gradient image. On the other hand, when thepartition is determined to be a non-rectangular partition, circuitry 160obtains the first prediction image as the prediction image without usingthe gradient image.

With this, encoder 100 can reduce use of a gradient image fornon-rectangular partitions, and suppress an increase in the processingamount. Accordingly, encoder 100 can efficiently process the imageblock.

For example, circuitry 160 determines that the partition is anon-rectangular partition when the partition is a triangular partition.With this, encoder 100 can suppress an increase in the processing amountfor triangular partitions.

For example, the prediction image obtained when the partition isdetermined not to be a non-rectangular partition is the same as aportion corresponding to the partition, of a prediction image obtainedfor the image block in a determined prediction mode. The predictionimage obtained for the image block in the determined prediction mode isa prediction image obtained for the image block without splitting theimage block into the plurality of partitions. The determined predictionmode may be predetermined.

With this, encoder 100 can obtain a prediction image for a rectangularpartition in the same manner as in the case of obtaining a predictionimage for the image block without splitting the image block into aplurality of partitions. Accordingly, encoder 100 can simplify theprocessing.

For example, circuitry 160 obtains the gradient image by applying afilter to the first prediction image to extract a difference valuebetween pixels. With this, encoder 100 can obtain an appropriategradient image for the first prediction image, and obtain an appropriatesecond prediction image using the appropriate gradient image.

FIG. 27 is a flow chart illustrating a third operation example ofencoder 100 illustrated in FIG. 24. For example, circuitry 160 includedin encoder 100 performs the operations illustrated in FIG. 27, usingmemory 162.

Specifically, circuitry 160 splits an image block into a plurality ofpartitions (S1131). Circuitry 160 then generates a motion vectorcandidate list for a partition included in the plurality of partitions(S1132).

Circuitry 160 then obtains a motion vector for the partition from themotion vector candidate list (S1133). Circuitry 160 then performs interprediction processing for the partition using the motion vector for thepartition (S1134). Circuitry 160 then encodes the image block using theresult of the inter prediction processing (S1135).

For example, when generating the motion vector candidate list, circuitry160 determines whether the partition is a non-rectangular partition.

When the partition is determined not to be a non-rectangular partition,circuitry 160 generates the motion vector candidate list. When doing so,circuitry 160 uses at least one motion vector among a plurality ofmotion vectors for a plurality of spatially neighboring partitions thatspatially neighbor the partition, a plurality of motion vectors for aplurality of temporally neighboring partitions that temporally neighborthe partition, and a plurality of motion vectors for a plurality ofsub-partitions included in the partition.

Even when the partition is determined to be a non-rectangular partition,circuitry 160 generates the motion vector candidate list. However, whendoing so, circuitry 160 does not use the plurality of motion vectors forthe plurality of sub-partitions, but uses at least one motion vectoramong the plurality of motion vectors for the plurality of spatiallyneighboring partitions and the plurality of motion vectors for theplurality of temporally neighboring partitions.

Here, the plurality of spatially neighboring partitions are partitionsthat spatially neighbor the partition. The plurality of temporallyneighboring partitions are partitions that temporally neighbor thepartition. The plurality of sub-partitions are included in thepartition.

With this, encoder 100 can reduce use, for non-rectangular partitions,of a plurality of motion vectors for a plurality of sub-partitions, andsuppress an increase in the processing amount. Accordingly, encoder 100can efficiently process the image block.

For example, circuitry 160 determines that the partition is anon-rectangular partition when the partition is a triangular partition.With this, encoder 100 can suppress an increase in the processing amountfor triangular partitions.

For example, the plurality of motion vectors for the plurality ofsub-partitions include motion vectors predicted from motion vectors forregions which spatially or temporally neighbor the plurality ofsub-partitions. With this, encoder 100 can use a motion vector which ispredicted, as a motion vector for a sub-partition, from a motion vectorfor a region neighboring the sub-partition.

For example, the motion vector candidate list generated when thepartition is determined not to be a non-rectangular partition is thesame as a motion vector candidate list generated for the image block ina determined prediction mode. With this, encoder 100 can generate themotion vector candidate list for a rectangular partition in the samemanner as in the case of generating a motion vector candidate list forthe image block. Accordingly, encoder 100 can simplify the processing.The determined prediction mode may be predetermined.

For example, each of the plurality of temporally neighboring partitionsis a co-located partition which, in a picture different from a picturethat includes the partition, is located in a position that correspondsto a position of the partition. With this, encoder 100 can use themotion vector for the co-located partition as a motion vector for thetemporally neighboring partition.

FIG. 28 is a block diagram illustrating an implementation example ofdecoder 200. Decoder 200 includes circuitry 260 and memory 262. Forexample, the plurality of constituent elements of decoder 200illustrated in FIG. 10 are implemented by circuitry 260 and memory 262illustrated in FIG. 28.

Circuitry 260 is electronic circuitry accessible to memory 262, andperforms information processing. For example, circuitry 260 is exclusiveor general electronic circuitry which decodes a video using memory 262.Circuitry 260 may be a processor such as a CPU. Circuitry 260 may be anaggregate of a plurality of electronic circuits.

Moreover, for example, circuitry 260 may perform the functions of two ormore constituent elements among the plurality of constituent elements ofdecoder 200 illustrated in FIG. 10, except the constituent elements thatstore information. In other words, circuitry 260 may perform theabove-described operations as the operations of the two or moreconstituent elements.

Memory 262 is an exclusive or general memory for storing informationused by circuitry 260 to decode a video. Memory 262 may be an electroniccircuit, may be connected to circuitry 260, or may be included incircuitry 260.

Memory 262 may be an aggregate of a plurality of electronic circuits, ormay be configured in the form of a plurality of sub-memories. Memory 262may be a magnetic disc, an optical disc, or the like, or may beexpressed as storage, a recording medium, or the like. Memory 262 may bea non-volatile memory or a volatile memory.

For example, memory 262 may perform the functions of, among theplurality of constituent elements of decoder 200 illustrated in FIG. 10,the constituent elements that store information. Specifically, memory262 may perform the functions of block memory 210 and frame memory 214illustrated in FIG. 10.

Moreover, memory 262 may store a bitstream corresponding to an encodedvideo, or may store a decoded video. Memory 262 may store a program forcausing circuitry 260 to decode a video.

Note that not all of the plurality of constituent elements illustratedin FIG. 10 need to be implemented by decoder 200, and not all of theprocesses described above need to be performed by decoder 200. Some ofthe constituent elements illustrated in FIG. 10 may be included inanother device, and some of the processes described above may beperformed by another device. An image block can be efficiently processedby decoder 200 implementing some of the constituent elements illustratedin FIG. 10 and performing some of the processes described above.

FIG. 29 is a flow chart illustrating a first operation example ofdecoder 200 illustrated in FIG. 28. For example, circuitry 260 includedin decoder 200 performs the operation illustrated in FIG. 29, usingmemory 262. Specifically, circuitry 260 decodes an image block (S1211).

For example, when decoding the image block, circuitry 260 obtains one ormore size parameters related to the size of the image block. Circuitry260 then determines whether the one or more size parameters and one ormore thresholds satisfy a determined relationship. The determinedrelationship may be predetermined.

Circuitry 260 then decodes a split parameter when the one or more sizeparameters and the one or more thresholds are determined to satisfy thedetermined relationship. Here, the split parameter indicates whether theimage block is to be split into a plurality of partitions including anon-rectangular partition. Circuitry 260 then decodes the image blockafter splitting the image block into the plurality of partitions whenthe split parameter indicates that the image block is to be split intothe plurality of partitions.

With this, decoder 200 can switch whether or not to split the imageblock into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters related to the size ofthe image block and the one or more thresholds satisfy the determinedrelationship. Accordingly, decoder 200 can efficiently process the imageblock.

For example, circuitry 260 decodes the image block without decoding thesplit parameter when the one or more size parameters and the one or morethresholds are determined not to satisfy the determined relationship.With this, the coding amount can be reduced. Moreover, decoder 200 canreduce the amount of processing for decoding the split parameter.

For example, circuitry 260 decodes the image block without splitting theimage block or decodes the image block after splitting the image blockinto a plurality of rectangular partitions, when the one or more sizeparameters and the one or more thresholds are determined not to satisfythe determined relationship. With this, decoder 200 can reduce splittingof the image block into a plurality of partitions including anon-rectangular partition.

For example, circuitry 260 decodes the image block without splitting theimage block or decodes the image block after splitting the image blockinto a plurality of rectangular partitions, when the split parameterindicates that the image block is not to be split into the plurality ofpartitions. With this, decoder 200 can reduce splitting of the imageblock into a plurality of partitions including a non-rectangularpartition.

For example, the one or more thresholds comprise one threshold. Thedetermined relationship is that each of the one or more size parametersis greater than or equal to the one threshold, or that at least one ofthe one or more size parameters is greater than or equal to the onethreshold. With this, decoder 200 can switch whether or not to split theimage block into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters are greater than orequal to the one threshold.

For example, the one or more thresholds comprise a first threshold and asecond threshold, and the first threshold is less than or equal to thesecond threshold. The determined relationship is that each of the one ormore size parameters is greater than or equal to the first threshold andless than or equal to the second threshold, or that at least one of theone or more size parameters is greater than or equal to the firstthreshold and less than or equal to the second threshold. With this,decoder 200 can switch whether or not to split the image block into aplurality of partitions including a non-rectangular partition, when theone or more size parameters are greater than or equal to the firstthreshold and less than or equal to the second threshold.

For example, the non-rectangular partition is a triangular partition.With this, decoder 200 can switch whether or not to split the imageblock into a plurality of partitions including a triangular partition,when the one or more size parameters related to the size of the imageblock and the one or more thresholds satisfy the determinedrelationship.

For example, the one or more size parameters include at least one of aratio of the width of the image block to the height of the image block,a ratio of the height of the image block to the width of the imageblock, the width of the image block, or the height of the image block.With this, decoder 200 can use, as a size parameter, at least one of theratio of the width to the height of the image block, the ratio of theheight to the width of the image block, the width of the image block, orthe height of the image block.

For example, each of the one or more thresholds is greater than or equalto zero. With this, decoder 200 can switch whether or not to split theimage block into a plurality of partitions including a non-rectangularpartition, when the one or more size parameters and the one or morethresholds, each of which is greater than or equal to zero, satisfy thedetermined relationship.

For example, the one or more thresholds indicate a restricted range of aratio of the width of the image block to the height of the image block.Here, the restricted range is a range for splitting the image block intothe plurality of partitions. With this, decoder 200 can switch whetheror not to split the image block into a plurality of partitions includinga non-rectangular partition, when the one or more size parameters andthe one or more thresholds, which indicate a restricted range of theratio of the width to the height, satisfy the determined relationship.

FIG. 30 is a flow chart illustrating a second operation example ofdecoder 200 illustrated in FIG. 28. For example, circuitry 260 includedin decoder 200 performs the operations illustrated in FIG. 30, usingmemory 262. For example, circuitry 260 splits an image block into aplurality of partitions (S1221). Circuitry 260 then obtains a predictionimage for a partition included in the plurality of partitions (S1222).Circuitry 260 then decodes the image block using the prediction image(S1223).

For example, when obtaining the prediction image, circuitry 260determines whether the partition is a non-rectangular partition.

Here, when the partition is determined not to be a non-rectangularpartition, circuitry 260 obtains a first prediction image for thepartition using a first motion vector for the partition. Then, circuitry260 obtains a second motion vector for the partition using the firstprediction image, and obtains a second prediction image for thepartition as the prediction image using the second motion vector.

On the other hand, when the partition is determined to be anon-rectangular partition, circuitry 260 obtains the first predictionimage as the prediction image using the first motion vector, withoutusing the second motion vector.

With this, decoder 200 can reduce the two-step operation fornon-rectangular partitions, and suppress an increase in the processingamount. Accordingly, decoder 200 can efficiently process the imageblock.

For example, circuitry 260 determines that the partition is anon-rectangular partition when the partition is a triangular partition.With this, decoder 200 can suppress an increase in the processing amountfor triangular partitions.

For example, the prediction image obtained when the partition isdetermined not to be a non-rectangular partition is the same as aportion corresponding to the partition, of a prediction image obtainedfor the image block in a determined prediction mode. The predictionimage obtained for the image block in the determined prediction mode isa prediction image obtained for the image block without splitting theimage block into the plurality of partitions. The determined predictionmode may be predetermined.

With this, decoder 200 can obtain a prediction image for a rectangularpartition in the same manner as in the case of obtaining a predictionimage for the image block without splitting the image block into aplurality of partitions. Accordingly, decoder 200 can simplify theprocessing.

For example, circuitry 260 obtains the second motion vector byperforming motion estimation using the first prediction image. Withthis, decoder 200 can obtain an appropriate second motion vector usingthe first prediction image, and obtain an appropriate second predictionimage using the appropriate second motion vector.

For example, when obtaining the prediction image, circuitry 260determines whether the partition is a non-rectangular partition.

Here, when the partition is determined not to be a non-rectangularpartition, circuitry 260 obtains (i) a first prediction image for thepartition, (ii) a gradient image for the first prediction image, and(iii) a second prediction image as the prediction image using the firstprediction image and the gradient image. On the other hand, when thepartition is determined to be a non-rectangular partition, circuitry 260obtains the first prediction image as the prediction image without usingthe gradient image.

With this, decoder 200 can reduce use of a gradient image fornon-rectangular partitions, and suppress an increase in the processingamount. Accordingly, decoder 200 can efficiently process the imageblock.

For example, circuitry 260 determines that the partition is anon-rectangular partition when the partition is a triangular partition.With this, decoder 200 can suppress an increase in the processing amountfor triangular partitions.

For example, the prediction image obtained when the partition isdetermined not to be a non-rectangular partition is the same as aportion corresponding to the partition, of a prediction image obtainedfor the image block in a determined prediction mode. Here, theprediction image obtained for the image block in the determinedprediction mode is a prediction image obtained for the image blockwithout splitting the image block into the plurality of partitions. Thedetermined prediction mode may be predetermined.

With this, decoder 200 can obtain a prediction image for a rectangularpartition in the same manner as in the case of obtaining a predictionimage for the image block without splitting the image block into aplurality of partitions. Accordingly, decoder 200 can simplify theprocessing.

For example, circuitry 260 obtains the gradient image by applying afilter to the first prediction image to extract a difference valuebetween pixels. With this, decoder 200 can obtain an appropriategradient image for the first prediction image, and obtain an appropriatesecond prediction image using the appropriate gradient image.

FIG. 31 is a flow chart illustrating a third operation example ofdecoder 200 illustrated in FIG. 28. For example, circuitry 260 includedin decoder 200 performs the operations illustrated in FIG. 31, usingmemory 262.

For example, circuitry 260 splits an image block into a plurality ofpartitions (S1231). Circuitry 260 then generates a motion vectorcandidate list for a partition included in the plurality of partitions(S1232).

Circuitry 260 then obtains a motion vector for the partition from themotion vector candidate list (S1233). Circuitry 260 then performs interprediction processing for the partition using the motion vector for thepartition (S1234). Circuitry 260 then decodes the image block using theresult of the inter prediction processing (S1235).

For example, when generating the motion vector candidate list, circuitry260 determines whether the partition is a non-rectangular partition.

When the partition is determined not to be a non-rectangular partition,circuitry 260 generates the motion vector candidate list. When doing so,circuitry 260 uses at least one motion vector among a plurality ofmotion vectors for a plurality of spatially neighboring partitions thatspatially neighbor the partition, a plurality of motion vectors for aplurality of temporally neighboring partitions that temporally neighborthe partition, and a plurality of motion vectors for a plurality ofsub-partitions included in the partition.

Even when the partition is determined to be a non-rectangular partition,circuitry 260 generates the motion vector candidate list. However, whendoing so, circuitry 260 does not use the plurality of motion vectors forthe plurality of sub-partitions, but uses at least one motion vectoramong the plurality of motion vectors for the plurality of spatiallyneighboring partitions and the plurality of motion vectors for theplurality of temporally neighboring partitions.

Here, the plurality of spatially neighboring partitions are partitionsthat spatially neighbor the partition. The plurality of temporallyneighboring partitions are partitions that temporally neighbor thepartition. The plurality of sub-partitions are included in thepartition.

With this, decoder 200 can reduce use, for non-rectangular partitions,of a plurality of motion vectors for a plurality of sub-partitions, andsuppress an increase in the processing amount. Accordingly, decoder 200can efficiently process the image block.

For example, circuitry 260 determines that the partition is anon-rectangular partition when the partition is a triangular partition.With this, decoder 200 can suppress an increase in the processing amountfor triangular partitions.

For example, the plurality of motion vectors for the plurality ofsub-partitions include motion vectors predicted from motion vectors forregions which spatially or temporally neighbor the plurality ofsub-partitions. With this, decoder 200 can use a motion vector which ispredicted, as a motion vector for a sub-partition, from a motion vectorfor a region neighboring the sub-partition.

For example, the motion vector candidate list generated when thepartition is determined not to be a non-rectangular partition is thesame as a motion vector candidate list generated for the image block ina determined prediction mode. With this, decoder 200 can generate themotion vector candidate list for a rectangular partition in the samemanner as in the case of generating a motion vector candidate list forthe image block. Accordingly, decoder 200 can simplify the processing.The determined prediction mode may be predetermined.

For example, each of the plurality of temporally neighboring partitionsis a co-located partition which, in a picture different from a picturethat includes the partition, is located in a position that correspondsto a position of the partition. With this, decoder 200 can use themotion vector for the co-located partition as a motion vector for thetemporally neighboring partition.

[Supplemental Information]

Encoder 100 and decoder 200 according to the present embodiment may beused as an image encoder and an image decoder, respectively, or may beused as a video encoder and a video decoder, respectively.

Alternatively, each of encoder 100 and decoder 200 can be used as aprediction device or an inter prediction device. That is to say, each ofencoder 100 and decoder 200 may correspond only to inter predictor 126and inter predictor 218. The other constituent elements such as entropyencoder 110 and entropy decoder 202 may be included in another device.

At least part of the present embodiment may be used as an encodingmethod, a decoding method, a prediction method, or another method.

In the present embodiment, each of the constituent elements may beconfigured in the form of an exclusive hardware product, or may beimplemented by executing a software program suitable for the constituentelement. Each of the constituent elements may be implemented by means ofa program execution unit, such as a CPU or a processor, reading andexecuting a software program recorded on a recording medium such as ahard disk or a semiconductor memory.

Specifically, encoder 100 and decoder 200 may each include processingcircuitry and storage electrically connected to the processing circuitryand accessible from the processing circuitry. For example, theprocessing circuitry corresponds to circuitry 160 or 260, and thestorage corresponds to memory 162 or 262.

The processing circuitry includes at least one of an exclusive hardwareproduct or a program execution unit, and performs processing using thestorage. When the processing circuitry includes a program executionunit, the storage stores a software program executed by the programexecution unit.

Here, the software for implementing, for example, encoder 100 or decoder200 according to the present embodiment is a program as follows: Theprogram causes a computer to perform an encoding method which includesencoding an image block. The encoding of the image block includes:obtaining one or more size parameters related to a size of the imageblock; determining whether the one or more size parameters and one ormore thresholds satisfy a determined relationship; encoding a splitparameter when the one or more size parameters and the one or morethresholds are determined to satisfy the determined relationship, thesplit parameter indicating whether the image block is to be split into aplurality of partitions including a non-rectangular partition; andencoding the image block after splitting the image block into theplurality of partitions when the split parameter indicates that theimage block is to be split into the plurality of partitions. Thedetermined relationship may be predetermined.

Alternatively, the program causes a computer to perform a decodingmethod which includes decoding an image block. The decoding of the imageblock includes: obtaining one or more size parameters related to a sizeof the image block; determining whether the one or more size parametersand one or more thresholds satisfy a determined relationship; decoding asplit parameter when the one or more size parameters and the one or morethresholds are determined to satisfy the determined relationship, thesplit parameter indicating whether the image block is to be split into aplurality of partitions including a non-rectangular partition; anddecoding the image block after splitting the image block into theplurality of partitions when the split parameter indicates that theimage block is to be split into the plurality of partitions. Thedetermined relationship may be predetermined.

Alternatively, the program causes a computer to perform an encodingmethod which includes: splitting an image block into a plurality ofpartitions; obtaining a prediction image for a partition included in theplurality of partitions; and encoding the image block using theprediction image. The obtaining of the prediction image includes:determining whether the partition is a non-rectangular partition; whenthe partition is determined not to be a non-rectangular partition,obtaining (i) a first prediction image for the partition using a firstmotion vector for the partition, (ii) a second motion vector for thepartition using the first prediction image, and (iii) a secondprediction image for the partition as the prediction image using thesecond motion vector; and when the partition is determined to be anon-rectangular partition, obtaining the first prediction image as theprediction image using the first motion vector, without using the secondmotion vector.

Alternatively, the program causes a computer to perform a decodingmethod which includes: splitting an image block into a plurality ofpartitions; obtaining a prediction image for a partition included in theplurality of partitions; and decoding the image block using theprediction image. The obtaining of the prediction image includes:determining whether the partition is a non-rectangular partition; whenthe partition is determined not to be a non-rectangular partition,obtaining (i) a first prediction image for the partition using a firstmotion vector for the partition, (ii) a second motion vector for thepartition using the first prediction image, and (iii) a secondprediction image for the partition as the prediction image using thesecond motion vector; and when the partition is determined to be anon-rectangular partition, obtaining the first prediction image as theprediction image using the first motion vector, without using the secondmotion vector.

Alternatively, the program causes a computer to perform an encodingmethod which includes: splitting an image block into a plurality ofpartitions; obtaining a prediction image for a partition included in theplurality of partitions; and encoding the image block using theprediction image. The obtaining of the prediction image includes:determining whether the partition is a non-rectangular partition; whenthe partition is determined not to be a non-rectangular partition,obtaining (i) a first prediction image for the partition, (ii) agradient image for the first prediction image, and (iii) a secondprediction image as the prediction image using the first predictionimage and the gradient image; and when the partition is determined to bea non-rectangular partition, obtaining the first prediction image as theprediction image without using the gradient image.

Alternatively, the program causes a computer to perform a decodingmethod which includes: splitting an image block into a plurality ofpartitions; obtaining a prediction image for a partition included in theplurality of partitions; and decoding the image block using theprediction image. The obtaining of the prediction image includes:determining whether the partition is a non-rectangular partition; whenthe partition is determined not to be a non-rectangular partition,obtaining (i) a first prediction image for the partition, (ii) agradient image for the first prediction image, and (iii) a secondprediction image as the prediction image using the first predictionimage and the gradient image; and when the partition is determined to bea non-rectangular partition, obtaining the first prediction image as theprediction image without using the gradient image.

Alternatively, the program causes a computer to perform an encodingmethod which includes: splitting an image block into a plurality ofpartitions; generating a motion vector candidate list for a partitionincluded in the plurality of partitions; obtaining a motion vector forthe partition from the motion vector candidate list; performing interprediction processing for the partition using the motion vector for thepartition; and encoding the image block using a result of the interprediction processing. The generating of the motion vector candidatelist includes: determining whether the partition is a non-rectangularpartition; when the partition is determined not to be a non-rectangularpartition, generating the motion vector candidate list using at leastone motion vector among a plurality of motion vectors for a plurality ofspatially neighboring partitions that spatially neighbor the partition,a plurality of motion vectors for a plurality of temporally neighboringpartitions that temporally neighbor the partition, and a plurality ofmotion vectors for a plurality of sub-partitions included in thepartition; and when the partition is determined to be a non-rectangularpartition, generating the motion vector candidate list using at leastone motion vector among the plurality of motion vectors for theplurality of spatially neighboring partitions and the plurality ofmotion vectors for the plurality of temporally neighboring partitions,without using the plurality of motion vectors for the plurality ofsub-partitions.

Alternatively, the program causes a computer to perform a decodingmethod which includes: splitting an image block into a plurality ofpartitions; generating a motion vector candidate list for a partitionincluded in the plurality of partitions; obtaining a motion vector forthe partition from the motion vector candidate list; performing interprediction processing for the partition using the motion vector for thepartition; and decoding the image block using a result of the interprediction processing. The generating of the motion vector candidatelist includes: determining whether the partition is a non-rectangularpartition; when the partition is determined not to be a non-rectangularpartition, generating the motion vector candidate list using at leastone motion vector among a plurality of motion vectors for a plurality ofspatially neighboring partitions that spatially neighbor the partition,a plurality of motion vectors for a plurality of temporally neighboringpartitions that temporally neighbor the partition, and a plurality ofmotion vectors for a plurality of sub-partitions included in thepartition; and when the partition is determined to be a non-rectangularpartition, generating the motion vector candidate list using at leastone motion vector among the plurality of motion vectors for theplurality of spatially neighboring partitions and the plurality ofmotion vectors for the plurality of temporally neighboring partitions,without using the plurality of motion vectors for the plurality ofsub-partitions.

It is noted that “at least one of A, B, and C” as used herein denotesthe conjunctive and the disjunctive, unless the context indicatesotherwise. For example, as disclosed herein, generating a motion vectorcandidate list using at least one motion vector among a plurality ofmotion vectors for a plurality of spatially neighboring partitions thatspatially neighbor the partition, a plurality of motion vectors for aplurality of temporally neighboring partitions that temporally neighborthe partition, and a plurality of motion vectors for a plurality ofsub-partitions included in the partition, includes generating a motionvector candidate list including a motion vector of a spatiallyneighboring partition, without including a motion vector of a temporallyneighboring partition.

The constituent elements may be circuits as described above. Thecircuits may constitute circuitry as a whole, or may be individualcircuits. Each constituent element may be implemented by a generalprocessor, or may be implemented by an exclusive processor.

Moreover, processing executed by a particular constituent element may beexecuted by another constituent element. The processing execution ordermay be modified, or a plurality of processes may be executed inparallel. Furthermore, an encoding and decoding device may includeencoder 100 and decoder 200.

The ordinal numbers such as “first” and “second” used in the descriptionmay be changed as appropriate. New ordinal numbers may be given to theconstituent elements, or the ordinal numbers of the constituent elementsmay be removed.

Although some aspects of encoder 100 and decoder 200 have been describedabove based on an embodiment, the aspects of encoder 100 and decoder 200are not limited to this embodiment. Various modifications to thisembodiment that are conceivable to those skilled in the art, as well asembodiments resulting from combinations of constituent elements indifferent embodiments, may be included within the scope of the aspectsof encoder 100 and decoder 200, so long as they do not depart from theessence of the present disclosure.

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, part ofthe processes in the flowcharts, part of the constituent elements of theapparatuses, and part of the syntax described in this aspect may beimplemented in combination with other aspects.

Embodiment 2

As described in each of the above embodiments, each functional block cantypically be realized as an MPU and memory, for example. Moreover,processes performed by each of the functional blocks are typicallyrealized by a program execution unit, such as a processor, reading andexecuting software (a program) recorded on a recording medium such asROM. The software may be distributed via, for example, downloading, andmay be recorded on a recording medium such as semiconductor memory anddistributed. Note that each functional block can, of course, also berealized as hardware (dedicated circuit).

Moreover, the processing described in each of the embodiments may berealized via integrated processing using a single apparatus (system),and, alternatively, may be realized via decentralized processing using aplurality of apparatuses. Moreover, the processor that executes theabove-described program may be a single processor or a plurality ofprocessors. In other words, integrated processing may be performed, and,alternatively, decentralized processing may be performed.

Embodiments and aspects of the present disclosure are not limited to theabove exemplary embodiments and aspects; various modifications may bemade to the exemplary embodiments and aspects, the results of which arealso included within the scope of the embodiments and aspects of thepresent disclosure.

Next, application examples of the moving picture encoding method (imageencoding method) and the moving picture decoding method (image decodingmethod) described in each of the above embodiments and a system thatemploys the same will be described. The system is characterized asincluding an image encoder that employs the image encoding method, animage decoder that employs the image decoding method, and an imageencoder/decoder that includes both the image encoder and the imagedecoder. Other configurations included in the system may be modified ona case-by-case basis.

[Usage Examples]

FIG. 32 illustrates an overall configuration of content providing systemex100 for implementing a content distribution service. The area in whichthe communication service is provided is divided into cells of desiredsizes, and base stations ex106, ex107, ex108, ex109, and ex110, whichare fixed wireless stations, are located in respective cells.

In content providing system ex100, devices including computer ex111,gaming device ex112, camera ex113, home appliance ex114, and smartphoneex115 are connected to internet ex101 via internet service providerex102 or communications network ex104 and base stations ex106 throughex110. Content providing system ex100 may combine and connect anycombination of the above elements. The devices may be directly orindirectly connected together via a telephone network or near fieldcommunication rather than via base stations ex106 through ex110, whichare fixed wireless stations. Moreover, streaming server ex103 isconnected to devices including computer ex111, gaming device ex112,camera ex113, home appliance ex114, and smartphone ex115 via, forexample, internet ex101. Streaming server ex103 is also connected to,for example, a terminal in a hotspot in airplane ex117 via satelliteex116.

Note that instead of base stations ex106 through ex110, wireless accesspoints or hotspots may be used. Streaming server ex103 may be connectedto communications network ex104 directly instead of via internet ex101or internet service provider ex102, and may be connected to airplaneex117 directly instead of via satellite exl16.

Camera ex113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex115 is a smartphone device,cellular phone, or personal handyphone system (PHS) phone that canoperate under the mobile communications system standards of the typical2G, 3G, 3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex118 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex103 via, for example, base stationex106. When live streaming, a terminal (e.g., computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, orairplane ex117) performs the encoding processing described in the aboveembodiments on still-image or video content captured by a user via theterminal, multiplexes video data obtained via the encoding and audiodata obtained by encoding audio corresponding to the video, andtransmits the obtained data to streaming server ex103. In other words,the terminal functions as the image encoder according to one aspect ofthe present disclosure.

Streaming server ex103 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, andterminals inside airplane ex117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed datadecode and reproduce the received data. In other words, the devices eachfunction as the image decoder according to one aspect of the presentdisclosure.

[Decentralized Processing]

Streaming server ex103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client is dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times. In the event of, for example, some kind ofan error or a change in connectivity due to, for example, a spike intraffic, it is possible to stream data stably at high speeds since it ispossible to avoid affected parts of the network by, for example,dividing the processing between a plurality of edge servers or switchingthe streaming duties to a different edge server, and continuingstreaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene-by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real-time streaming.

In another example, camera ex113 or the like extracts a feature amountfrom an image, compresses data related to the feature amount asmetadata, and transmits the compressed metadata to a server. Forexample, the server determines the significance of an object based onthe feature amount and changes the quantization accuracy accordingly toperform compression suitable for the meaning of the image. Featureamount data is particularly effective in improving the precision andefficiency of motion vector prediction during the second compressionpass performed by the server. Moreover, encoding that has a relativelylow processing load, such as variable length coding (VLC), may behandled by the terminal, and encoding that has a relatively highprocessing load, such as context-adaptive binary arithmetic coding(CABAC), may be handled by the server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mall, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos and the server, on a per-unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real-time.

Moreover, since the videos are of approximately the same scene,management and/or instruction may be carried out by the server so thatthe videos captured by the terminals can be cross-referenced. Moreover,the server may receive encoded data from the terminals, change referencerelationship between items of data or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Moreover, the server may stream video data after performing transcodingto convert the encoding format of the video data. For example, theserver may convert the encoding format from MPEG to VP, and may convertH.264 to H.265.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

[3D, Multi-Angle]

In recent years, usage of images or videos combined from images orvideos of different scenes concurrently captured or the same scenecaptured from different angles by a plurality of terminals such ascamera ex113 and/or smartphone ex115 has increased. Videos captured bythe terminals are combined based on, for example, theseparately-obtained relative positional relationship between theterminals, or regions in a video having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. Note that the server may separatelyencode three-dimensional data generated from, for example, a pointcloud, and may, based on a result of recognizing or tracking a person orobject using three-dimensional data, select or reconstruct and generatea video to be transmitted to a reception terminal from videos capturedby a plurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting, from three-dimensional datareconstructed from a plurality of images or videos, a video from aselected viewpoint. Furthermore, similar to with video, sound may berecorded from relatively different angles, and the server may multiplex,with the video, audio from a specific angle or space in accordance withthe video, and transmit the result.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyesand perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server superimposes virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information, and the server may generate superimposed data basedon three-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data includes, in addition to RGBvalues, an a value indicating transparency, and the server sets the avalue for sections other than the object generated fromthree-dimensional data to, for example, 0, and may perform the encodingwhile those sections are transparent. Alternatively, the server may setthe background to a determined RGB value, such as a chroma key, andgenerate data in which areas other than the object are set as thebackground. The determined RGB value may be predetermined.

Decoding of similarly streamed data may be performed by the client(i.e., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big-picture view as well as for each viewer tocheck his or her assigned area or inspect a region in further detail upclose.

In the future, both indoors and outdoors, in situations in which aplurality of wireless connections are possible over near, mid, and fardistances, it is expected to be able to seamlessly receive content evenwhen switching to data appropriate for the current connection, using astreaming system standard such as MPEG-DASH. With this, the user canswitch between data in real time while freely selecting a decoder ordisplay apparatus including not only his or her own terminal, but also,for example, displays disposed indoors or outdoors. Moreover, based on,for example, information on the position of the user, decoding can beperformed while switching which terminal handles decoding and whichterminal handles the displaying of content. This makes it possible to,while in route to a destination, display, on the wall of a nearbybuilding in which a device capable of displaying content is embedded oron part of the ground, map information while on the move. Moreover, itis also possible to switch the bit rate of the received data based onthe accessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal or when encoded data is copied to an edge server in a contentdelivery service.

[Scalable Encoding]

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 33, that is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments. The server may have a configuration in which contentis switched while making use of the temporal and/or spatial scalabilityof a stream, which is achieved by division into and encoding of layers,as illustrated in FIG. 33. Note that there may be a plurality ofindividual streams that are of the same content but different quality.In other words, by determining which layer to decode up to based oninternal factors, such as the processing ability on the decoder side,and external factors, such as communication bandwidth, the decoder sidecan freely switch between low resolution content and high resolutioncontent while decoding. For example, in a case in which the user wantsto continue watching, at home on a device such as a TV connected to theinternet, a video that he or she had been previously watching onsmartphone ex115 while on the move, the device can simply decode thesame stream up to a different layer, which reduces server side load.

Furthermore, in addition to the configuration described above in whichscalability is achieved as a result of the pictures being encoded perlayer and the enhancement layer is above the base layer, the enhancementlayer may include metadata based on, for example, statisticalinformation on the image, and the decoder side may generate high imagequality content by performing super-resolution imaging on a picture inthe base layer based on the metadata. Super-resolution imaging may beimproving the SN ratio while maintaining resolution and/or increasingresolution. Metadata includes information for identifying a linear or anon-linear filter coefficient used in super-resolution processing, orinformation identifying a parameter value in filter processing, machinelearning, or least squares method used in super-resolution processing.

Alternatively, a configuration in which a picture is divided into, forexample, tiles in accordance with the meaning of, for example, an objectin the image, and on the decoder side, only a partial region is decodedby selecting a tile to decode, is also acceptable. Moreover, by storingan attribute about the object (person, car, ball, etc.) and a positionof the object in the video (coordinates in identical images) asmetadata, the decoder side can identify the position of a desired objectbased on the metadata and determine which tile or tiles include thatobject. For example, as illustrated in FIG. 34, metadata is stored usinga data storage structure different from pixel data such as an SEImessage in HEVC. This metadata indicates, for example, the position,size, or color of the main object.

Moreover, metadata may be stored in units of a plurality of pictures,such as stream, sequence, or random access units. With this, the decoderside can obtain, for example, the time at which a specific personappears in the video, and by fitting that with picture unit information,can identify a picture in which the object is present and the positionof the object in the picture.

[Web Page Optimization]

FIG. 35 illustrates an example of a display screen of a web page on, forexample, computer ex111. FIG. 36 illustrates an example of a displayscreen of a web page on, for example, smartphone ex115. As illustratedin FIG. 35 and FIG. 36, a web page may include a plurality of imagelinks which are links to image content, and the appearance of the webpage differs depending on the device used to view the web page. When aplurality of image links are viewable on the screen, until the userexplicitly selects an image link, or until the image link is in theapproximate center of the screen or the entire image link fits in thescreen, the display apparatus (decoder) displays, as the image links,still images included in the content or I pictures, displays video suchas an animated gif using a plurality of still images or I pictures, forexample, or receives only the base layer and decodes and displays thevideo.

When an image link is selected by the user, the display apparatusdecodes giving the highest priority to the base layer. Note that ifthere is information in the HTML code of the web page indicating thatthe content is scalable, the display apparatus may decode up to theenhancement layer. Moreover, in order to guarantee real timereproduction, before a selection is made or when the bandwidth isseverely limited, the display apparatus can reduce delay between thepoint in time at which the leading picture is decoded and the point intime at which the decoded picture is displayed (that is, the delaybetween the start of the decoding of the content to the displaying ofthe content) by decoding and displaying only forward reference pictures(I picture, P picture, forward reference B picture). Moreover, thedisplay apparatus may purposely ignore the reference relationshipbetween pictures and coarsely decode all B and P pictures as forwardreference pictures, and then perform normal decoding as the number ofpictures received over time increases.

[Autonomous Driving]

When transmitting and receiving still image or video data such two- orthree-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., includingthe reception terminal is mobile, the reception terminal can seamlesslyreceive and decode while switching between base stations among basestations ex106 through ex110 by transmitting information indicating theposition of the reception terminal upon reception request. Moreover, inaccordance with the selection made by the user, the situation of theuser, or the bandwidth of the connection, the reception terminal candynamically select to what extent the metadata is received or to whatextent the map information, for example, is updated.

With this, in content providing system ex100, the client can receive,decode, and reproduce, in real time, encoded information transmitted bythe user.

[Streaming of Individual Content]

In content providing system ex100, in addition to high image quality,long content distributed by a video distribution entity, unicast ormulticast streaming of low image quality, short content from anindividual is also possible. Moreover, such content from individuals islikely to further increase in popularity. The server may first performediting processing on the content before the encoding processing inorder to refine the individual content. This may be achieved with, forexample, the following configuration.

In real-time while capturing video or image content or after the contenthas been captured and accumulated, the server performs recognitionprocessing based on the raw or encoded data, such as capture errorprocessing, scene search processing, meaning analysis, and/or objectdetection processing. Then, based on the result of the recognitionprocessing, the server-either when prompted or automatically edits thecontent, examples of which include: correction such as focus and/ormotion blur correction; removing low-priority scenes such as scenes thatare low in brightness compared to other pictures or out of focus; objectedge adjustment; and color tone adjustment. The server encodes theedited data based on the result of the editing. It is known thatexcessively long videos tend to receive fewer views. Accordingly, inorder to keep the content within a specific length that scales with thelength of the original video, the server may, in addition to thelow-priority scenes described above, automatically clip out scenes withlow movement based on an image processing result. Alternatively, theserver may generate and encode a video digest based on a result of ananalysis of the meaning of a scene.

Note that there are instances in which individual content may includecontent that infringes a copyright, moral right, portrait rights, etc.Such an instance may lead to an unfavorable situation for the creator,such as when content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Moreover, the server may be configuredto recognize the faces of people other than a registered person inimages to be encoded, and when such faces appear in an image, forexample, apply a mosaic filter to the face of the person. Alternatively,as pre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background be processed, and the server may process the specifiedregion by, for example, replacing the region with a different image orblurring the region. If the region includes a person, the person may betracked in the moving picture, and the head region may be replaced withanother image as the person moves.

Moreover, since there is a demand for real-time viewing of contentproduced by individuals, which tends to be small in data size, thedecoder first receives the base layer as the highest priority andperforms decoding and reproduction, although this may differ dependingon bandwidth. When the content is reproduced two or more times, such aswhen the decoder receives the enhancement layer during decoding andreproduction of the base layer and loops the reproduction, the decodermay reproduce a high image quality video including the enhancementlayer. If the stream is encoded using such scalable encoding, the videomay be low quality when in an unselected state or at the start of thevideo, but it can offer an experience in which the image quality of thestream progressively increases in an intelligent manner. This is notlimited to just scalable encoding; the same experience can be offered byconfiguring a single stream from a low quality stream reproduced for thefirst time and a second stream encoded using the first stream as areference.

[Other Usage Examples]

The encoding and decoding may be performed by LSI ex500, which istypically included in each terminal. LSI ex500 may be configured of asingle chip or a plurality of chips. Software for encoding and decodingmoving pictures may be integrated into some type of a recording medium(such as a CD-ROM, a flexible disk, or a hard disk) that is readable by,for example, computer ex111, and the encoding and decoding may beperformed using the software. Furthermore, when smartphone ex115 isequipped with a camera, the video data obtained by the camera may betransmitted. In this case, the video data is coded by LSI ex500 includedin smartphone ex115.

Note that LSI ex500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content or when the terminalis not capable of executing a specific service, the terminal firstdownloads a codec or application software then obtains and reproducesthe content.

Aside from the example of content providing system ex100 that usesinternet ex101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments may be implemented in a digital broadcasting system. Thesame encoding processing and decoding processing may be applied totransmit and receive broadcast radio waves superimposed with multiplexedaudio and video data using, for example, a satellite, even though thisis geared toward multicast whereas unicast is easier with contentproviding system ex100.

[Hardware Configuration]

FIG. 37 illustrates smartphone ex115. FIG. 38 illustrates aconfiguration example of smartphone ex115. Smartphone ex115 includesantenna ex450 for transmitting and receiving radio waves to and frombase station ex110, camera ex465 capable of capturing video and stillimages, and display ex458 that displays decoded data, such as videocaptured by camera ex465 and video received by antenna ex450. Smartphoneex115 further includes user interface ex466 such as a touch panel, audiooutput unit ex457 such as a speaker for outputting speech or otheraudio, audio input unit ex456 such as a microphone for audio input,memory ex467 capable of storing decoded data such as captured video orstill images, recorded audio, received video or still images, and mail,as well as decoded data, and slot ex464 which is an interface for SIMex468 for authorizing access to a network and various data. Note thatexternal memory may be used instead of memory ex467.

Moreover, main controller ex460 which comprehensively controls displayex458 and user interface ex466, power supply circuit ex461, userinterface input controller ex462, video signal processor ex455, camerainterface ex463, display controller ex459, modulator/demodulator ex452,multiplexer/demultiplexer ex453, audio signal processor ex454, slotex464, and memory ex467 are connected via bus ex470.

When the user turns the power button of power supply circuit ex461 on,smartphone ex115 is powered on into an operable state by each componentbeing supplied with power from a battery pack.

Smartphone ex115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex460, whichincludes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex456 is converted into a digital audiosignal by audio signal processor ex454, and this is applied with spreadspectrum processing by modulator/demodulator ex452 and digital-analogconversion and frequency conversion processing by transmitter/receiverex451, and then transmitted via antenna ex450. The received data isamplified, frequency converted, and analog-digital converted, inversespread spectrum processed by modulator/demodulator ex452, converted intoan analog audio signal by audio signal processor ex454, and then outputfrom audio output unit ex457. In data transmission mode, text,still-image, or video data is transmitted by main controller ex460 viauser interface input controller ex462 as a result of operation of, forexample, user interface ex466 of the main body, and similar transmissionand reception processing is performed. In data transmission mode, whensending a video, still image, or video and audio, video signal processorex455 compression encodes, via the moving picture encoding methoddescribed in the above embodiments, a video signal stored in memoryex467 or a video signal input from camera ex465, and transmits theencoded video data to multiplexer/demultiplexer ex453. Moreover, audiosignal processor ex454 encodes an audio signal recorded by audio inputunit ex456 while camera ex465 is capturing, for example, a video orstill image, and transmits the encoded audio data tomultiplexer/demultiplexer ex453. Multiplexer/demultiplexer ex453multiplexes the encoded video data and encoded audio data using adetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex452 andtransmitter/receiver ex451, and transmits the result via antenna ex450.The determined scheme may be predetermined.

When video appended in an email or a chat, or a video linked from a webpage, for example, is received, in order to decode the multiplexed datareceived via antenna ex450, multiplexer/demultiplexer ex453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex455 via synchronous busex470, and supplies the encoded audio data to audio signal processorex454 via synchronous bus ex470. Video signal processor ex455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodiments,and video or a still image included in the linked moving picture file isdisplayed on display ex458 via display controller ex459. Moreover, audiosignal processor ex454 decodes the audio signal and outputs audio fromaudio output unit ex457. Note that since real-time streaming is becomingmore and more popular, there are instances in which reproduction of theaudio may be socially inappropriate depending on the user's environment.Accordingly, as an initial value, a configuration in which only videodata is reproduced, i.e., the audio signal is not reproduced, ispreferable. Audio may be synchronized and reproduced only when an input,such as when the user clicks video data, is received.

Although smartphone ex115 was used in the above example, threeimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. Further, inthe description of the digital broadcasting system, an example is givenin which multiplexed data obtained as a result of video data beingmultiplexed with, for example, audio data, is received or transmitted,but the multiplexed data may be video data multiplexed with data otherthan audio data, such as text data related to the video. Moreover, thevideo data itself rather than multiplexed data maybe received ortransmitted.

Although main controller ex460 including a CPU is described ascontrolling the encoding or decoding processes, terminals often includeGPUs. Accordingly, a configuration is acceptable in which a large areais processed at once by making use of the performance ability of the GPUvia memory shared by the CPU and GPU or memory including an address thatis managed so as to allow common usage by the CPU and GPU. This makes itpossible to shorten encoding time, maintain the real-time nature of thestream, and reduce delay. In particular, processing relating to motionestimation, deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of, for example pictures, all at once.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to, for example, televisionreceivers, digital video recorders, car navigation systems, mobilephones, digital cameras, digital video cameras, teleconferencingsystems, electronic mirrors, etc.

What is claimed is:
 1. An encoder, comprising: circuitry; and memory,wherein using the memory, the circuitry: obtains an image block from acoding tree unit (CTU); determines to perform first inter prediction orsecond inter prediction based on information on inter prediction, thefirst inter prediction including a bi-directional optical flow (BIO)process, the second inter prediction including a motion compensationprocess, the second inter prediction not including the BIO process; andencodes the image block based on the determined inter predictionprocess, wherein, when the BIO process is determined to be performed,the circuitry (i) obtains first prediction images for the image block,(ii) obtains gradient images for the first prediction images, and (iii)generates a prediction image for the image block using the firstprediction images and the gradient images, and when the motioncompensation process is determined to be performed, the circuitry (i)determines a plurality of partitions in the image block, (ii) obtains asecond prediction image for each of the plurality of partitions, and(iii) generates a prediction image for the image block using the secondprediction images, wherein, the information includes a flag.
 2. Adecoder, comprising: circuitry; and memory, wherein using the memory,the circuitry: obtains an image block from a coding tree unit (CTU);determines to perform first inter prediction or second inter predictionbased on information on inter prediction, the first inter predictionincluding a bi-directional optical flow (BIO) process, the second interprediction including a motion compensation process, the second interprediction not including the BIO process; and decodes the image blockbased on the determined inter prediction process, wherein, when the BIOprocess is determined to be performed, the circuitry (i) obtains firstprediction images for the image block, (ii) obtains gradient images forthe first prediction images, and (iii) generates a prediction image forthe image block using the first prediction images and the gradientimages, and when the motion compensation process is determined to beperformed, the circuitry (i) determines a plurality of partitions in theimage block, (ii) obtains a second prediction image for each of theplurality of partitions, and (iii) generates a prediction image for theimage block using the second prediction images, wherein, the informationincludes a flag.
 3. A non-transitory computer readable medium storing abitstream, the bitstream including information on inter predictionaccording to which a decoder determines to perform first interprediction or second inter prediction, the first inter predictionincluding a bi-directional optical flow (BIO) process, the second interprediction including a motion compensation process, the second interprediction not including the BIO process, wherein an image block isobtained from a coding tree unit (CTU), and in response to adetermination, based on the information on inter prediction, to performthe BIO process, (i) first prediction images for the image block areobtained; (ii) gradient images for the first prediction images areobtained; and (iii) a prediction image for the image block is generatedusing the first prediction images and the gradient images, and inresponse to a determination, based on the information on interprediction, to perform the motion compensation process, (i) a pluralityof partitions are determined in the image block; (ii) a secondprediction image is obtained for each of the plurality of partitions;and (iii) a prediction image for the image block is generated using thesecond prediction images, wherein, the information includes a flag.